Article Categories Archives: Lube Talk

Diesel Fuel Additives

By Dan Watson


Ultra-low sulfur diesel, low-sulfur diesel, off-road full-sulfur diesel, number 1 or number 2
diesel, Cetane ratings for diesel and on and on it goes; what does it all mean and do I need to
use an additive to supplement my diesel fuel? Today’s diesel fuel is very different from diesel
of 30 years ago. Modern ultra-low sulfur diesel is required in all over the road diesel vehicles,
and failure to comply with this requirement can result in costly fines. In this article, I will
explain the sulfur content ratings and how the sulfur content affects the fuel system
components. I will also take a look at Cetane ratings and why Cetane levels are important. And
finally, I will explore using diesel fuel additives…how they work and whether you should
consider using an additive.

Sulfur is a natural component of crude oil that is not refined out when making diesel. Special
processes are used to remove sulfur, and these extra steps in finishing diesel add cost to the
finished product. Original diesel of 30 years ago was limited to 5,000 ppm sulfur in solution. In
the early 1990’s, low-sulfur diesel set the sulfur limit to 500 ppm sulfur in solution. In October
2006, the ultra-low sulfur diesel limit of 15 ppm in solution was stipulated. The 15 ppm sulfur
limit was primarily designed to prevent poisoning the catalytic convertor and adding to the
clogging of the diesel particulate filter. Certainly, the 15 ppm limit would reduce sulfur based
exhaust compounds such as sulfur dioxide and sulfur trioxides. These sulfur compounds are
directly related to acid rain, so reducing them is a good idea. So, there is no turning back on
the quest to limit exhaust emissions and consequently reducing sulfur content in diesel fuel; the
question is, at what cost to fuel system components and to diesel performance?

Since removing sulfur has a positive effect on emissions, why make such a big deal about the
resulting effect on the fuel system components? The process for removing sulfur to such a low
level of 15 ppm also strips out the compounds that provide diesel lubricity. Sulfur is not the actual lubricant but sulfur compounds are, and effectively removing sulfur from diesel results in a very poor lubricity rating for the fuel. Fuel pumps and injectors are lubricated by diesel and nothing else, so without sulfur providing the lubricity, these components are not lubricated. This is well known by the diesel manufacturers and the government, and standards for adding lubricants to the diesel have been established. It is a subject of discussion as to whether the levels of added lubricant are sufficient to provide for acceptable long-life expectations.

Cetane number or CN is a measure of a fuel’s ignition delay, the time period between the start
of injection and the first identifiable pressure increase during combustion of the fuel. In a
particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower
cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils. In short,
the higher the cetane number the more easily the fuel will combust in a compression setting
(such as a diesel engine). The characteristic diesel “knock” occurs when the first portion of fuel
that has been injected into the cylinder suddenly ignites after an initial delay. Minimizing this
delay results in less unburned fuel in the cylinder at the beginning and less intense knock.
Therefore, higher-cetane fuel usually causes an engine to run more smoothly and quietly. This
does not necessarily translate into greater efficiency, although it may in certain engines.

Diesel comes in two classifications, number 1 and number 2. Number 1 diesel is more highly
refined (more waxes are removed) and is more resistant to freezing (becoming slush) than
number 2 diesel. Contrary to many assumptions, number 1 diesel is not required to have a
higher cetane number than number 2 diesel. In many cases, number 1 diesel does have a
higher cetane, but it is achieved by adding a cetane enhancing additive.

Generally, diesel engines operate well with a CN from 40 to 55. Fuels with higher cetane
numbers have shorter ignition delays, providing more time for the fuel combustion process to
be completed. Hence, higher speed diesel engines operate more effectively with higher cetane
number fuels. In North America, most states adopt ASTM D975 as their diesel fuel standard
and the minimum cetane number is set at 40, with typical values in the 42-45 range.

Clearly, it is relatively straight forward to see that using an additive to raise cetane level would
be dependent on the quality of fuel available. If diesel with proper cetane levels is available,
then you might not get much improvement by using a cetane enhancing additive. Another
consideration would be the expected RPM of the diesel engine being used. If the engine is
turbo charged and runs at higher RPM, then the higher cetane will be useful is enhancing

Traditional Fuel Injector Pintal


Traditional Fuel Injector

High-Pressure Common-Rail Fuel Injector Pintal




When evaluating diesel additives for improving lubricity of ultra-low sulfur diesel, it is important
to look at other factors involved in fuel system and cylinder maintenance and performance.
Injector performance is a matter of design and quality coupled with cleanliness. A perfectly
clean injector operating at design pressure can be very effective in providing fully atomized fuel
to the cylinder for combustion. Allow deposits or lacquer to build up in areas of critical
clearances and you have the formula for trouble. Injectors fire at pressures between 10,000 psi
and 30,000 psi, depending on application and manufacturer. The slightest impairment can
cause diminished performance. The optimum performance and efficiency takes place when
the injector provides a 360 degree puff of fully atomized fuel to combust fully with no
unburned fuel. Any liquid drops will be partially burned and result in high carbon waste and

For years, the industry has concentrated on the injector tips as the critical point to maintain as
clean as possible. Any buildup of carbon (coking) at the tip would be immediately detrimental
to the desired 360 degree puff and would allow a droplet to be formed. Cleaning agents have
been developed to keep the tips clean and they have been effective. Today, with the extremely
high pressure injectors being smaller and having tighter clearances internal diesel injector
deposits (often abbreviated to “IDID”) have been found within the injector body itself, such as
at the armature group, on the piston and nozzle needle and inside the nozzle body. These
deposits can slow the response of the fuel injector, or cause sticking of moving internal parts,
which may result in loss of control of injection event timing, as well as of the quantity of fuel
delivered per injection.

In summary, you may or may not need a cetane boost additive, but you probably do need an
additive for enhanced lubricity and detergency. The current fuel injectors are really modern
marvels, and, as incredible as they are, they are more susceptible to being fouled by carbon and
lacquer than the old fashioned injectors. The ramifications of poorly performing injectors are
significant: poor performance, loss of fuel economy and clogged diesel particulate exhaust
filters (DPF). Of course, the exhaust system is another story all in itself and I will not go down
that path in this article. When looking for a good detergent additive, make sure you see some
mention of the internal diesel injector deposits (often abbreviated to “IDID”); if the additive
doesn’t address this problem, don’t use it. With the cost of today’s injectors running $600 to
$800, using an appropriate additive is a very cost-effective strategy.

(407) 657-5969


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Bypass Filtration

By Dan Watson

The advanced exhaust system, including diesel particulate filters, urea injection systems, exhaust gas recirculation and catalytic converters is certainly a step forward in the reduction of emissions into our environment. These controls, however, come at a cost. In a future article, I will explain the how these advanced exhaust systems work.  In this article, I want to take a look at what recycled soot does to the engine oil in the diesel engine and recommend bypass oil filtration as a worthwhile protection for this considerable investment.

Oil bypass filters for large diesel engines are accepted as a necessity and have been recommended by several aftermarket filter companies for many years. As a certified lubrication specialist, I have recommended bypass filtration systems as a solution for many diesel applications, though not for every application. Prior to the advent of exhaust gas recirculation (EGR), diesel engines were capable of dealing with soot. Even if they could benefit from a bypass system, they could certainly get by without one. Not so with the new advanced exhaust systems and EGR.  I absolutely recommend bypass filtration for these engines.

What Is Bypass Filtration?

Bypass filtration refers to systems in which a portion of the oil pump output, usually no more than ten percent, is diverted to an auxiliary filter. The system is so-named because in a conventional bypass system, the oil bypasses the engine and returns to the oil pan without providing lubrication to the engine. In fact, some reference manuals refer to such systems as parasitic filtration systems. It is important to note that while the appellation is not totally without merit, bypass systems do not divert enough oil from the engine to fall below manufacturer’s specifications. There is also a second type of bypass system in which none of the oil is diverted from its flow through the engine – more on that later.

ByPass Filter

Courtsey of Amsoil Inc.

A typical single remote (parasitic) bypass filtration system diverts a fraction of the oil in order to remove smaller particles that the full flow filter misses.

The need for a bypass filtration system arises when the filtration provided by the stock, full flow oil filter is insufficient to remove enough of the oil’s contaminants. Because the standard filter must allow sufficient oil flow to the engine to keep it properly lubricated, the filter media inside are, by design, thin enough to allow the oil to flow relatively easily. Of course, it would be no good to make the standard filter media more dense – so that it could handle smaller particles – if this meant that the oil was hindered from getting to the engine. Nobody wants a molten mass of metal under the hood, no matter how clean it might be. This means that standard oil filters, even good ones, cannot deal with particles in the oil that are smaller than about 15 microns. A bypass filtration system, on the other hand – by only filtering approximately ten percent of the oil at a time and leaving the other 90 percent to do the lubrication work – complements the standard full flow oil filter and allows the overall lubrication system to both provide sufficient lubrication and filter smaller particles down to the three-micron range. Even though the bypass system only deals with a fraction of the oil on any given pass through the system, over time, the complete volume of oil is treated by the finer media in the oil bypass filters.


Soot is a byproduct of the combustion process that begins as particles that are sub-micron in size. At that size, they pose no threat to the engine and if they remained that size, there would be no need (and it would be very difficult) to filter them. Unfortunately, soot particles are attracted to one another and join together to form particles that are big enough to cause damage but small enough to evade capture by the full flow filter. Soot is more readily produced in diesel engines than gasoline engines.

Today’s turbo-charged, computer controlled, fuel injected engines are extremely good at mixing air and fuel for clean burning engines. Earlier turbo-charged diesel engines were as good, if not better, at burning cleanly; unfortunately, the requirements to lower emissions resulted in exhaust gas recirculation (EGR). Recirculation of exhaust brings up to 35% of soot back into the engine for re-burning. The soot levels for these engines are significantly higher than the preceding engines and the soot inevitably finds its way into the oil through the piston rings. High soot levels increase the viscosity of the oil and interfere with proper oil flow. When soot levels are high, soot begins to drop out of solution and can clog critical oil galleries and starve components of vital lubrication. The requirement to recirculate exhaust gases is one of the bases of the CJ-4 classification for diesel oils. CJ-4 rated diesel oils are designed to carry higher levels of soot and to resist soot dropping out of solution.

Soot's affects

Soot and other particles as small as five microns are responsible for the majority of abrasive wear in an engine. A good bypass oil filtration system will effectively remove particles to the three micron, and sometimes smaller, range.

Using CJ-4 oil in combination with the highest quality full flow filters will help keep soot in check to a point. However, the only way to ultimately remove the soot that remains unfiltered in a system is to drain the oil. This reality shortens the lifespan of oil and requires a higher frequency of oil changes than might otherwise be necessary, especially for extended drain synthetics. In the future, I believe that improvements in diesel oils and better full flow filters will allow for extended drain periods using the standard oil filter system. Using the technology available today, I recommend using a high quality synthetic CJ-4 diesel oil complemented by an oil bypass filters system that is capable of filtering out a portion of the soot. Excellent bypass systems remove 30 to 40 percent of the soot. Even at this level of efficiency, soot levels are manageable. Full flow filters by themselves essentially remove no soot from the system.

Variations of Oil Bypass Filters

Most bypass filtration systems leave the standard full flow filter in place and add a remotely-located bypass filter. These systems are the ones sometimes referred to as parasitic because they divert some of the oil away from the main oil flow responsible for the lubrication of the engine’s components. The amount of oil diverted is controlled by an orifice or similar restrictor to make sure that enough oil is reaching the engine. An alternate design, patented by Amsoil, locates both the full flow and bypass filter remotely.

The Amsoil dual remote filtration system eliminates the parasitic loss of oil flow to the engine.


This dual remote oil filtration system eliminates the parasitic characteristic of a typical bypass unit by routing all the oil, whether it travels through the full flow filter or through the oil bypass filter, to the engine components after filtration has occurred. As with the single remote bypass filter system, only a fraction of the oil travels through the bypass filter on a given pass.

Regardless of the design or manufacturer, the bypass system is a good investment on any diesel engine. For the modern diesel engine, with EGR, the bypass is a necessity. Soot is a concern in all diesel engines but with the EGR system, soot levels can become destructive. A potential benefit of installing a bypass filtration system is extended oil change intervals. When using properly formulated synthetic diesel oil and a high quality bypass filtration system, it is possible to avoid the impact of higher soot levels and extend oil drain intervals significantly. If you own a turbo diesel with EGR, you are simply protecting your investment by installing a good bypass oil filtration system.
(407) 657-5969

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Engine Oil Filtration

Oil Filters

By Dan Watson

I have spent the past several issues of Tow Professional explaining oils and how they lubricate.  Understanding the fundamentals of lubrication and selecting the proper lubricant is certainly the primary responsibility of the maintenance personnel. Once that choice is made, it is now necessary to insure the oil is as clean as possible to function to the highest level to provide protection for the operating equipment.

First, let’s take a look at how engine oil gets contaminated and understand exactly what we are trying to filter out of the oil as it is in use.


Dust and Dirt

The quality and design limitations, especially the proper fit and seal of air cleaners and crankcase ventilation systems, allow a certain level of dust and dirt into the engine.  Intake systems, including the structure supporting the air filter and the turbo charger, can permit unfiltered air to enter the engine. Proper maintenance of the engine and its accessories can minimize the amount of contaminants entering the lubrication system.

Metal Particles

Normal wear of engine parts produces very small metal particles that are picked up and circulated by the oil. Particles of road dust and dirt increase wear rates and generate larger, even more abrasive metal particles that are circulated through the engine by the oil. While oil filters help keep these particles at a minimum, they can’t remove them entirely.

Combustion By-Products

Soot and Carbon

Incomplete combustion produces soot, carbon and other deposit-forming materials. An engine running too “rich,” or with too much fuel, increases contaminant levels.

Soot is a natural product of diesels engines; ultra-low sulfur diesel coupled with improved turbo control of intake-air has reduced the level of carbon soot produced by modern diesel engines.  Unfortunately, the requirement for exhaust gas recirculation (EGR) creates a high soot load for the diesel engine oil.  Light-load, low-speed gasoline engine operation and high-load, low-speed diesel engine operation increase levels of these combustion by-products.

Realizing that it is impossible to avoid the engine oil becoming contaminated, it is obvious that finding effective filtration mechanisms is critical to achieving desired engine life.  There are two methods of filtering engine oil: Full Flow filtration and Bypass (Side Stream or Parallel) filtration.

Full Flow Filtration

Full-flow oil filters install directly into the line of oil circulation; the oil passes through the filter as it travels between the oil pump and the engine (see Figure 1). A full-flow oil filter must remove and hold contaminants without obstructing oil flow to the engine.

Because they use a thin layer of porous filter paper, most oil filters on the market compromise the filtration of finer materials. Such filters have almost no extended cleaning ability because they have a low capacity for storing dirt.

These “surface-type” paper filters quickly become restricted as debris builds up on the paper surface, forcing the filter by-pass valve to open and allow unfiltered oil into the engine.

Illustration of Normal Oil Flow

By-Pass Oil Filtration

Because oil must be filtered quickly while removing most of the particles, the average full-flow filter can only trap particles as small as 20 microns. By-pass oil filtration uses a secondary filter (see Figure 2), with the purpose of eliminating nearly all contaminants in engine oil. By-pass filters have high capacities and eliminate much smaller particles than full-flow filters, including those in the 2 to 20 micron range, soot and sludge.

* Courtesies of Amsoil Inc.

Oil Circulation using an AMSOIL Spin-On By-Pass Filter

Illustration of By-Pass Filtration

By-pass filters operate by filtering oil on a “partial-flow” basis. They draw approximately 10 percent of the oil pump’s capacity at any one time and trap the extremely small, wear-causing contaminants that full-flow filters can’t remove. The continual process eventually makes all the oil analytically clean, reducing long-term wear and helping extend oil life.

Filter Ratings

Filter media is the heart and soul of the oil filter; regardless of how you construct the filter, if the media is inefficient at removing contaminates the filter is junk.  No matter how much I dress up a Donkey, I can’t make that Donkey a Thorough Bred race horse. With filter media, performance is all that matters; you get what you pay for.

Filtration is measured in percent efficiency at removing particles of certain sizes. For example, a filter may be rated as nominal at 40 microns; this means the filter removes a nominated amount of contaminate, by weight for the rating. Inconsistent methods of determining a nominal rating has resulted in nominal as being virtually useless as a rating. Absolute rating, on the other hand, is very accurate and useful in rating filters.  Absolute is defined as: the cut-off point, which refers to the diameter of the largest spherical glass particle, normally expressed in micrometers (mm), which will pass through the filter under laboratory conditions. In simpler terms, no particle larger than the absolute micron rating should get through the filter. In the real world, this is not completely true, so a system of establishing filter efficiency has been established.

* Courtesies of Amsoil Inc.

Establishing a Beta ratio is done by dividing the number of particles of a particular size in the upstream flow by the number of particles of the same size in the downstream flow:

where bx is the beta ratio for contaminant larger than x mm (microns)
Nu is the number of particles larger than x mm (microns) per unit of volume upstream
Nd is the number of particles larger than x mm (microns) per unit of volume downstream.

The beta ratio is an indicator of how well a filter controls particulate; i.e., if one out of every two particles (>x microns) in the fluid pass through the filter, the beta ratio at x microns is 2; if one out of every 200 of the particles (>x microns) pass through the filter the beta ratio is 200.

Therefore, filters with a higher beta ratio retain more particles and have higher efficiency.

Efficiency for a given particle size (Ex) can be derived directly from the beta ratio by the following equation:

The following table lists some selected beta ratios and the correspondent efficiency:

b value to x microns

Cumulate efficiency %


for particles x micron












Filters have to store contaminates removed, and this is referred to as capacity. It is not easy to find an actual capacity rating, but you can determine how many miles the filter can be used before it must be changed. The longer the filter is allowed to be used represents how much debris the manufacturer has designed the filter to store.

Flow Rate

Measured in gallons per minute (GPM) is determined by the engine manufacturer for proper lubrication of the engine. Most full flow oil filters must pass a minimum of 9 gpm, some larger diesels require more flow, so rely on your owner’s manual to specify only filters that meet the flow rate.

To select filters for your equipment, you should research the filter ratings on various filters. It may be hard to find the information you are looking for on the filter packaging. You should be able to research online at the manufacturer’s website and find the filter ratings. Look for ratings in absolute not nominal, and, in some cases, you may find beta ratings. Beta ratings are not likely to be found for auto and truck filters; they usually are there for hydraulic and industrial filters. Synthetic filter media is superior to cellulose and much less susceptible to streaming and medial failure. A superior filter will have an absolute efficiency of greater than 98% for 20 micron particles and a mileage rating greater than the recommended oil change interval.

Never change your oil without changing your oil filter. Dirty oil is abrasive and will shorten the life of your engine.

In the next issue, I will discuss the advantages of bypass filtration and explain why it is so necessary for modern diesel engines.

If you come to the Florida Tow Show in April, stop by the Amsoil booth and say hello.
(407) 657-5969

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Grease, the Forgotten Lube

By Dan Watson

Bearings - Lube Talk

In previous Lube Talk articles, we looked at the role lubricants play in overcoming the effects of friction. In this installment, I want to examine one specialized type of lubricant: grease lube. Looking at previous civilizations, we can see that man has tried several methods to provide basic lubrication to load-bearing surfaces; axles have presented one of the most challenging applications. As far back as 1400 BC, mutton fat and beef tallow were used on chariot axles to reduce friction in order to allow for more speed and to slow down wear. One can only imagine the pressure on the maintenance men to make the chariot go faster and to avoid axles catching on fire from the continuous friction. While there is evidence of lime being added to these fats in order to make their lubricating properties last longer, few other improvements to the composition of grease are known to have been used until we reach the magic year of 1859.

What happened in 1859? Colonel Drake drilled the first ever oil well in Pennsylvania; since then, the world has not been the same. In petroleum oil, man found a lubricant that could be manipulated in a variety of ways to produce greases much superior to the lubricants that preceded them. In turn, more advanced and effective greases have been produced in recent decades with the advent of synthetic greases.

The word grease is derived from the Latin word Crassus meaning fat. We can see where the name came from (mutton fat, beef tallow); however, grease lube, for modern purposes, is not to be construed as fat. The American Society for Testing Materials (ASTM) defined grease in 1916 as: A solid to semi-fluid product of dispersion of a thickening agent in a liquid lubricant. In plain English, this means a lubricant composed of lubricating fluids (oils), thickened by mixing chemicals to produce a semi-fluid to semi-solid consistency.

Now that we know a little of the history of grease and how grease is defined in modern lubrication; when, where and why is grease lube used? While lubricating oils are able to lubricate any friction-causing situation, greases offer unique characteristics that are well suited for:

  • Situations requiring less dripping or spattering of lubricant
  • Hard to lubricate bearings or joints where reducing frequency of lubrication is needed
  • In dirty, dusty or hazardous environments where additional sealing is needed to prevent lubricant contamination
  • For intermittent operation. Oil drains away from critical bearings when the equipment is stopped but grease stays in place.

Grease Lube Composition

Greases are made from oil and thickeners (sometimes called soaps). The process is simple, but the details are fairly complex. The lubricating oil can be petroleum or synthetic and can vary in viscosity. Additionally, anti-wear and extreme pressure additives can be added to formulate greases for specific applications, such as high speed bearings, very cold or very hot conditions, open gears, extreme loads or high moisture conditions, to name a few. Oil and thickeners can be combined to offer greater temperature ranges and resistance to moisture. Thickeners can be combined or formulated with additional chemicals to produce more complex thickeners for specific applications.

Greases will vary in thickness depending on the amount and type of thickeners used, as well as the viscosity of the lubricating oil used. The National Lubricating Grease Institute (NLGI) is the regulating body that establishes specific ratings for greases. Greases are rated on a hardness scale from 000 to 6; where 000 is a thick liquid, like pudding, and 6 is a block, similar to hard clay. Today, 000 grease lube is used as a replacement for gear lubes in bearings and differentials, and number 6 grease is used where a rubbing action is needed to produce a light film on the surface to be lubricated. Wheel bearings and chassis greases used in auto and truck applications are usually NLGI #2. In very cold climates, NLGI #1 grease is preferred because the grease will thicken in response to the temperatures. Synthetic greases thickened with appropriate compounds are functional over a wide temperature range, from minus 50ºF to 500ºF; petroleum greases are generally limited to 0°F to 300°F.

In 1991, the NLGI developed a classification system specifically targeting automotive greases (Table One). For the majority of readers, it is the appropriate rating system for your truck applications.

Application NLGI
Service Limitations


Mild duty, frequent re-lubrication


Infrequent re-lubrication, high loads, water exposure
Wheel Bearings


Mild duty
Wheel Bearings


Moderate duty, typical of most vehicles
Wheel Bearings


Severe duty, high temperatures, frequent stop and go service

So, when you are looking to purchase grease lube for your truck, look for grease labeled GC-LB: grease rated for severe duty for the wheel bearings as well as for the chassis. Multi-purpose grease is the correct match for 3500 chassis, but heavy duty grease is the better choice for most tow trucks.  Synthetic greases, available from Amsoil and Mobil, will provide the best protection over the widest temperature range. Heavy duty grease is moly-fortified (molybdenum disulfide), which provides for extreme pressure lubrication. I have explained the difference in extreme pressure lubrication vs. standard lubrication regimes in an earlier issue of Lube Talk, so please refer to that issue for the specific explanation. There are several legitimate extreme pressure grease points on heavy duty trucks; using the correct grease is critical for proper operation and long life.

If the grease will be exposed to water, either by submersion or by spray, using water resistant grease is the best choice. To be water resistant, the grease must pass additional testing that insures its ability to cling to a surface while being sprayed with a stream of water. Water resistant greases contain additional thickeners and tackifiers that allow them to resist washing out. Sometimes, these greases will be labeled “marine,” but more and more they are simply referred to as water resistant.

Grease Compatibility

A word of caution; not all greases are compatible with each other. This problem occurs because some of the thickening agents chemically react with others, which can lead to the grease lube becoming very hard or liquefying or preventing the oil from leeching out to provide lubrication, essentially rendering the grease useless. Most grease you find for automotive applications are lithium or lithium-complex greases: these are compatible with each other. Table Two covers compatibility/incompatibility of commonly used greases. If you find grease that uses a different thickener than those listed, contact me to verify compatibility.

Compatibility / Incompatibility of Commonly Used greases (Table Two)

Compatibility / Incompatibility of Commonly Used greases

Table Two – Different types of grease lube are not always compatible with each other. For instance, the first two grease compounds, Aluminum Complex and Barium Complex are incompatible as indicated by the “I” inside a red box. A “C” inside a green box indicates that the two compounds are compatible with each other. A “B” in a yellow field indicates the two compounds possess only borderline compatibility.

Grease is the forgotten lubricant, it just doesn’t rise to the level of notice of other lubricants; however, grease lube is fundamental to proper care for your vehicle. For most auto or truck applications, greasing should be done at three month intervals for petroleum and six month intervals for synthetics. Wheel bearings properly packed with synthetic grease are good for 10 years, but the most convenient time for repacking is when the brakes are replaced. There are few manufacturers stipulating wheel bearing maintenance, and some are now installing sealed bearings that cannot be greased. Ball joints and steering joints can still be greased in most heavy duty vehicles, but in light duty vehicles, the grease fittings may not be installed and you will have to purchase them and install them. As with all lubricants, synthetic greases outperform petroleum greases, and the cost difference is actually in favor of the synthetics; you simply use less grease over time and the upfront cost difference is minimal.

For questions and/or comments, contact me via my website,, or by email at

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Automatic Transmission Fluid

By Dan Watson

Automatic Transmission Fluids (ATF) are the most complex fluids used in today’s vehicles. These complexly designed fluids perform multiple functions including:

  • Lubrication
  • Wear protection
  • Heat dissipation
  • Foam prevention
  • Shift quality optimization
  • Hydraulics
  • Material compatibility
Exterior 2011 Allison Transmission

The exterior of the 2011 Allison transmission hides a very complex assembly of various types of gears, O-rings, clutch faces, gaskets, seals and more.

To make ATF formulation even more complex, companies that produce automatic transmission fluid must align their products with all the different-from-each-other requirements specified by vehicle manufacturers. The following list is only a sample of the wide variations in the market place.

  • General Motors: Dexron III to Dexron VI
  • Chrysler: ATF-plus to ATF-4plus
  • Ford: Mercon, Mercon V, Mercon SP and Mercon LV
  • Allison Transmissions: C-4, C-5 and TES-389
  • Toyota: TO-4 and WS
  • Honda: Z-1 and CVT
  • Nissan: Nissan Matic-D, J and K

This is only a fraction of all the manufacturers’ specifications – and the list grows more and more ever year. As a vehicle owner, you must insure that the proper ATF is used in your vehicle by paying attention to your owner’s manual. Proper ATF in your automatic transmission is the key to the proper operation and life of your transmission. Simply put, using the wrong ATF may cause it to shift improperly and incompatible material may begin to deteriorate.

Understanding Your Automatic Transmission

If we take a more in-depth look at the functions listed above and how these are critical to proper transmission performance and life, it should be clear that using the specified ATF is imperative.

ATF Lubrication
Automatic transmissions contain hundreds of moving parts, including bearings, gears and sliding mechanisms. Multiple lubrication regimes (see “Intro to Lubrication“) and a fluid that lubricates over a wide range is required. The bearings require light weight oils that are designed for high speed applications in which the gears require oils capable of protecting the gears at the gear tooth interface.

ATF Wear
Proper lubrication is the key to reducing wear. Wear protection is established by the correct anti-wear additives, as well as the strength and stability of the oil used as the base stock. Again, what makes this challenging is the wide range of lubrication regimes that occur inside an automatic transmission.

Heat Dissipation
Heat is the No. 1 factor in transmission failures in modern vehicles. High pressure fluid and heat produced by the interaction of transmission gears causes automatic transmissions to build up heat; this is especially true under heavy loads. The ATF fluid is the major medium of heat transfer to remove the heat from the transmission. Air flow over the transmission will provide additional heat removal, but the modern aerodynamics of vehicles limits the airflow and so increases the heat load on the fluid.

Automatic transmissions use hydraulic actuation to move gears into different ratios, resulting in different vehicle speeds. Clutches are engaged and disengaged using hydraulic pressure, as well. Without hydraulics might be nearly impossible to construct the modern automatic transmission.

It is always counterproductive for lubricating oils to foam, since foamy oil does not establish a working oil film for protection. For hydraulic oils, it is fundamental for proper operation; foam is compressible and defeats the principle of pressurized oil performing work. Simply, foaming will limit or stop hydraulic actuation.

Material Compatibility
Various materials are used in automatic transmissions components: O-rings, clutch faces, gaskets and seals. Automatic transmission fluids must be compatible with all of these component materials or damage will cause operational problems that will lead to transmission failures.

A look inside the GM Six-Speed Hydramatic Transmission

A look inside the GM Six-Speed Hydramatic Transmission

Shift Quality
As if all the specifications required to satisfy the complex lubrication and functional aspects of automatic transmission fluid were not enough, each manufacturer requires different shifting characteristics – some manufacturers require a soft shift and others a hard shift – along with vastly different load bearing requirements. Some transmissions are four-speeds and many now are six-, seven- or eight-speed; each of these configurations creates varying geometric arrangements that affect component size and stress. So, there really is a legitimate reason why the different manufacturers develop tailored specifications for their transmissions; the transmissions are different and designed specifically for their line of vehicles.

Choosing the Right Automatic Transmission Fluid (ATF)

So, with all this information on the complexity of automatic transmission fluid, what should the consumer look for when buying ATF the next time the transmission needs serviced? The best approach is to systematically match your vehicle’s needs to the correct ATF and then find the best quality ATF for your application. Here are some steps to follow:

Step One: Check your owner’s manual to see what is specified for your vehicle. This is the most critical step in the selection process. Get this wrong and you could damage your transmission and incur expensive transmission repairs. Be especially attentive to the manufacturers’ specifications (eg: Dexron VI, Mercon V, Chrysler ATF+4 etc.). If you are having the service done at a service center, ask questions about the ATF. Some change centers seem to think ATF is ATF and they put the same fluid in every car.

Step Two: Acquire the necessary gaskets and filters required to change the transmission oil. If you are having the service done at a service center, ask questions about the changing of filters; some change centers do not change filters unless you direct them to do so. Internal transmission filters should be changed at least at 100,000 miles (I personally recommend every time the transmission fluid is changed).

Step Three: Choose between a complete transmission exchange or the traditional drop-the-pan and method. I do not like the idea of leaving used fluid in the transmission and mixing new, clean fluid with the old, dirty fluid. Certainly, it costs more for the exchange, but transmission repairs are the most expensive repair that will be done in the life of the vehicle and doing anything that will extend the life of the transmission just makes good sense.

Synthetic Vs Petroleum ATF

Should you use synthetic or petroleum automatic transmission fluid? This really is a straightforward analysis and the facts will lead to a correct decision. The easiest and most sensible approach is to compare the use of synthetic vs. petroleum for each of the stated functions of ATF.

Lubrication: Proper lubrication depends on both the base stock and additives to provide lubrication throughout the complete operating range of the transmission. Transmissions operate from cold to very hot, and the thermal properties of synthetics vs. petroleum results in a clear advantage for synthetics. Synthetic base stocks offer very wide temperature ranges with little effect on viscosity, while petroleum base stocks are not thermally stable, thinning at high temperature and thickening at low temperature.
Advantage: Synthetic

Wear Protection: Wear is directly related to additives and oil viscosity. As previously explained, synthetic oils maintain viscosity over wide temperature ranges, where petroleum oils change viscosity significantly over the same temperature range. Assuming the anti-wear additives are equal, the superior thermal stability of synthetic oils results in a far superior anti-wear performance for synthetic automatic transmission fluids.
Advantage: Synthetic

Heat Dissipation: In liquid state, the heat transfer quality for the synthetic ATF and the petroleum ATF is nearly equal. Synthetic oils will remain liquid at very high temperatures, where petroleum oils will thin and begin to flash to vapor at high temperatures. When the petroleum oils reach the point of flashing to vapor or being a mixed vapor liquid combination, heat dissipation is severely reduced.
Advantage: Synthetic

Foam Prevention: When lubricants foam, their ability to lubricate properly and prevent wear is significantly reduced. Additionally, foaming of fluids used in hydraulics prevents proper hydraulic action. Air is compressible and oil is not, so any amount of air in the hydraulic system will cause erratic operation. With proper additives, antifoaming of synthetic and petroleum based is virtually equal. Poor anti-foaming additives will allow for foaming regardless of the base stocks employed.
Advantage: None

Hydraulics: The movement of gears and engagement of clutches in the transmission is accomplished by hydraulics. Hydraulic systems use compressed oil to move pistons, and this, in turn, moves components to establish various gear ratios. When oil is operating at very high temperatures, flashing to vapor occurs. Vapor is compressible, and, for hydraulics to work, the medium (oil) cannot be compressible. Synthetic oils will tolerate much higher temperatures than petroleum oils before losing viscosity and flashing to vapor. The higher temperature range gives synthetic oils a superior hydraulic function at high temperatures. At very low temperatures, petroleum oils are similar to pudding, where synthetics are less viscous.
Advantage: Synthetic

GM Vortex Transmission Flex Gear

GM Vortex Transmission Flex Gear

Shift Quality: The engagement of the clutches and the gears in the automatic transmission is dependent on design and friction additives in the oil. Original equipment manufacturers will design the transmission for the shift of their choice, from very soft to very hard. Friction modifiers are the main elements controlling the shift quality. Synthetic or petroleum, the shift is a function of design and additives.
Advantage: None

Material Compatibility: Gaskets, O-Rings and clutch material must be compatible with the automatic transmission fluid including the additives. Modern materials are compatible with both petroleum and synthetic fluids with little difference.
Advantage: None

And the Winner is…

Looking at the functions established for automatic transmission fluids, synthetic fluids are superior in four of the seven functions, while petroleum fluids are superior in none. For three of the seven functions, there is no advantage of one fluid type over the other. This analysis results in a clear advantage for synthetic automatic transmission fluid.

When purchasing ATF for your vehicle, be sure to meet the specific requirements stipulated by your vehicle’s manufacturer. Today’s transmissions are incredibly complex mechanisms and, correspondingly, the automatic transmission fluid that they require can be very specific. Misapplication can cause expensive repairs. Synthetic transmission fluids will provide superior performance over a wide range of applications and extend the life of your transmission.

For questions and/or comments, contact me via my website,, or by email at

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Gear Lubes

By Dan Watson

In this issue of Lube Talk, I will respond to the numerous questions I receive from month to month about gear lubes. From the questions I receive, I realize that folks are not really sure what gear lubes are or exactly why they are different from motor oils. I want to briefly introduce gear lubes and discuss their classification system. Then, we will look at proper applications for gear lubes.

First, a little knowledge of gears is important in order to understand the function of gear lubes (please refer to Figure One for this discussion). Gears transmit motion and power from one rotating shaft to another rotating shaft, providing multiple applications of power transmission.

There are several types and various geometric shapes for gears, but I will only address automotive applications. In Figure One, spur gears, bevel gears and hypoid gears are displayed; sun and planetary gears will be discussed with automatic transmission systems. Spur gears are simple gears with easily meshing gear teeth that transfer power between parallel shafts. Bevel gears allow intersecting shafts to transmit power. Hypoid gears facilitate the transfer of power between non-intersecting shafts at right angles. The important concept to grasp in these gear sets is the action of contact and sliding motion. The spur and bevel gears are engaging and rolling in motion, whereas the pinion and ring in the hypoid gears are contacting and sliding. This sliding action allows the Hypoid gears to transmit greater power (the force is distributed over the sliding area), providing for smaller differentials in auto and truck applications.

Gear Types (graphic courtesy Amsoil)

Gear Lube

Gear Lube

Design and Function of Petroleum/Synthetic Gear Oil

With this summary introduction to gears, we can now go forward with the design and function of gear lubes. Gear lubes must achieve the following:

  • Provide for proper shifting in manual transmissions at all temperatures
  • Maintain fluid separation of moving metal surfaces
  • Reduce friction and wear
  • Lubricate associated bearings
  • Prevent scoring of highly stressed gears
  • Provide fluid flow in cold temperatures
  • Remove heat during operation to maintain safe temperatures
  • Demulsify (separate from water)
  • Prevent rust and corrosion
  • Resist foaming and dissipate entrained air bubbles
  • Be compatible with all seals


Gear lube is a complex product accomplishing a multitude of functions, and if any of these functions are ignored, it can result in damage to the components.

Classification of Petroleum and Synthetic Gear Oil

The American Petroleum Institute (API) establishes the service classifications for transportation gear lubes as follows:

  • GL-1 through GL-3 designates gear lubes for light loads on spiral and bevel gears. This classification is usually satisfied by motor oil.
  • GL-4 designates the type of service characteristics of gears, particularly hypoid, in passenger cars and other automotive equipment operated under high speed/ low torque and low speed/high torque conditions.
  • GL-5 designates the type of service characteristics of gears, particularly hypoid, in passenger cars and other automotive equipment operated under high speed/shock load, high speed/low torque, and low speed/high torque conditions.

The Society of Automotive Engineers (SAE) establishes the system to classify gear lubes by viscosity grades. The exact values for the viscosity grades are beyond the scope of this article; however, understanding the designation is important. Gear Lubes use a designation such as 75W-90 to indicate the viscosity grade. The 75W is the winter rating, and it establishes the cold weather performance of the lubricant. The 90 is the operational viscosity (measured at 210ºF). The lower the W number, the better the lube oil functions in cold weather. The higher the second number, the more viscous (thicker) the oil.

Manufacturers stipulate the required GL and SAE classifications for a particular gear set. The recommendation is based on the geometry (spur, bevel, hypoid etc.), as well as on the load and environmental conditions.

Automotive applications usually come down to transmissions and differentials. Materials used in the construction of the components like transmission synchronizers can require different types of additives in the gear lubes.

Gear Lubes are formulated by selecting base oils from petroleum or, in the case of synthetic gear oil lubes, synthetic oils and then adding in specific chemicals to achieve the rated classification. The additives consist of anti-wear, anti-foaming, anti-oxidation, demulsifiers, corrosion inhibitors, friction modifiers, viscosity improvers and extreme pressure additives and specialty additives where required. The specific formulations are determined by the manufacturer, and all gear lubes are not created equal.

OEMs (Original Equipment Manufacturers) determine the required gear lubes for the gear sets in their manufactured products. You can find the specified gear lube listed in the owner’s manual, and, in general, this is the gear lube you should use. Look for a viscosity rating, like 75W-90, and a classification, such as GL-4 or GL-5.

A classic error made by consumers is to buy thicker gear lube in order to get “better” protection. While there are times when using a 75W-140 or 75W-110 instead of the specified 75W-90 is appropriate, such a change should only be made on the advice of a lubrication professional. The failure rate for gears is very low, but the failure rate for bearings is not so low. Bearings are better lubricated by thinner oils, so the change to a thicker lube in the gears increases the likelihood of bearing failures. Towing is a heavy duty use of the vehicle, and, depending on the combined gross vehicle weight (including trailer), it may be prudent to use a heavier weight gear lube. The action of shifting transmission gears can hammer the gears in the differential when pulling heavy loads. Thicker gear lubes provide better shock absorption at the gear face and prevent spooning or cupping gear teeth. Some gear lube manufacturers have started to offer 75W-110 in order to provide better protection when pulling heavy loads without sacrificing as much fuel efficiency as 75W-140. If you plan to use your vehicle for heavy towing, my advice is to not guess. Contact a lubrication specialist and get the recommendation that is right for your vehicle and your driving conditions.

The transmission is nothing like the differential and rarely will GL-5 gear lube be required. When there is a gear lube specification, it will routinely be for GL-4. GL-4 gear lubes contain less extreme pressure (EP) additives and are suitable for brass alloys. Some transmissions use brass synchronizers and the sulfur-based EP additives can react with brass and destroy the synchronizers. A great many manual transmissions are now using automatic transmission fluid or motor oil. Others even use certain synchromesh fluids developed by the manufacturers. The best policy is to stick with the recommendations of the transmission manufacturer.

Petroleum or Synthetic Gear Oil?

When selecting gear lubes for your vehicle, you will have to choose between petroleum and synthetic gear oil. There is no argument in the lubrication profession over this question; synthetic gear oil is overwhelmingly superior in every category measured. Large trucking companies, like UPS for instance, use nothing but synthetic gear oil for better fuel economy and to extend equipment life.

In a future article, I will provide an in-depth comparison between petroleum and synthetic gear oil.

For questions and/ or comments, contact me via my website,, or by email at

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Synthetic vs. Petroleum

By Dan Watson

The ongoing march to achieve more technologically advanced engines continues, and certainly the modern turbo-charged diesel engine exemplifies that quest. The race between GM, Ford and Dodge has benefited you and me; the improvement in all aspects of these diesel engines is easily quantifiable in terms of horsepower and torque, as well as fuel efficiency and endurance.

Recognizing how vastly improved these diesels are to their predecessors, it should not surprise anyone that advances in the lubricants for these engines have also facilitated quantum leaps in performance.

Any oil, properly rated for use in a high performance turbo-charged engine, is a remarkable lubricant regardless of the base oil used. In this article, I will compare synthetic diesel engine oil to petroleum diesel engine oil and draw some conclusions and make some recommendations. Previous articles have established fundamentals of lubrication and how oil is made, so if you haven’t read those, a review might be in order. I am writing this article assuming you have read the preceding articles.

To start, we should compare several performance criteria for petroleum oil vs. synthetic oil.

Thermal Stability

How well does the oil hold viscosity as temperature increases? This is reflected in the Viscosity Index (VI) rating, with a higher number indicating greater stability. Petroleum oils rarely exceed 100 on the Viscosity Index, while some synthetics rate higher than 180. Oils that maintain rated viscosity – instead of thinning out at higher temperatures – perform better in your engine. Thin oil will reduce film strength and result in higher wear rates of critical engine parts.

Thermal Stability Advantage: Strong for Synthetic Oil

Viscosity Index

Higher viscosity index (VI) liquids are less responsive to temperature extremes. At 0°F, the VI 95 petroleum oil is thicker (measured in centistokes, a dynamic measure of resistance-to-flow) than the synthetic oil with a VI of 150. On the hot side at 210°F, the VI 150 synthetic maintains viscosity better than the VI 95 petroleum oil that thins out more easily.

Temperature Range

What are the highest and lowest temperatures the oil can tolerate and still provide proper lubrication, during continuous or intermittent duty? This range is established by measuring the pour point (lowest temperature the oil will pour) and the highest temperature at which the oil can hold sufficient viscosity in order to provide lubrication. Chart Two demonstrates the superior performance of synthetic oil vs. petroleum oil. Group III hydro-cracked synthetics are not on the graph, and it is important to note that the Group III synthetics will have similar cold flow performance but significantly less high temperature performance compared to Polyalphaolefins (PAO). PAO and Dibasic Acid Esters are the primary chemicals used in engine and drive line oils. A strong temperature range is paramount to providing proper lubrication, especially in severe duty or extreme temperatures.

Temperature Range Advantage: Very Strong for Synthetic Oil

Oil Temp vs. Synthetics

Oxidation Stability

How well does the oil resist oxidation and sludge formation? As oil oxidizes, it thickens (viscosity increases) and deposits sludge in the engine. Sludge may eventually clog critical oil passages, preventing necessary oil from reaching vital engine parts. This causes excessive wear and, eventually, failure of various engine parts. Synthetics are inert, meaning there are no polar sites (having positive or negative polarity) and simply do not react with oxygen. Petroleum oils are highly polar (mostly positive polarity) and readily react with oxygen. To counter this reactivity, petroleum oils are treated with anti-oxidation additives. When oils are operating in the intermittent range (temporarily outside the normal operating band), they are susceptible to higher rates of oxidation. Unfortunately, today’s engines are forcing oils to operate routinely at 230°F to 250°F. This puts the petroleum oils in a range of temperatures that causes increased use of the anti-oxidants in the additive package and shortens the life of the oil. PAO or Ester based synthetics are in the normal operating band for temperatures in excess of 330°F and suffer little or no oxidation. This is one of the reasons you hear of mechanics reporting how clean engines with synthetics are, even those with high mileage.

Oxidation Stability Advantage: Very Strong for Synthetics


How easily does the oil vaporize or boil off? When oils are hot, vaporization can result in significant oil consumption and thickening of the oil. Not only is this a problem for oil consumption, but the oil vapor is sucked into the engine via the Positive Crankcase Ventilation system, contributing to significant hydrocarbons in the exhaust (PCV systems have been used in gasoline engines and are now starting to be used in diesel engines). In petroleum oils, the molecular structure is non-uniform, consisting of various size compounds. Imagine countless footballs, baseballs, hockey sticks and tennis rackets all mixed together, pushing against each other. When the oil gets hot, some of the lightweight items are liberated and fly away while the larger, heavier items remain. As this process continues, only the larger items remain, resulting in much thicker oil. In contrast, the molecular structure of synthetics is like a bunch of identical golf balls, all the same size and tightly packed together, resisting vaporization; as a result, they stay in grade for much longer periods and reduce oil consumption.

Volatility Advantage: Strong for Synthetics


How does the oil affect the seals? Will it cause them to shrink or to swell? And, is the oil chemically compatible with them? Seals are made of a variety of compounds in order to provide rigid but flexible surfaces that promote good sealing in order to keep liquids in and dirt out. Petroleum oils are fully compatible with the seal materials used in modern engines and will slightly swell the seals. While PAO synthetics tend to shrink seals, Esters tend to swell the seals: both are chemically compatible. In synthetics where PAO is the primary base oil, another synthetic oil, Diester for example, is used to provide the desired seal swell and nourishment for seals. Historically, seal compatibility issues have caused real and imaginary problems for synthetic oils in the market place. Currently, seal issues for properly blended synthetic oils are no longer an issue.

Seals Advantage: Slight for Petroleum

Lubrication/Wear Protection

How well does the oil lubricate and, in turn, prevent wear? Lubrication is a result of both base oil and additive combinations performing in various lubrication regimes in order to prevent metal-to-metal contact and the wear that results. Where fluid film is retained, the base oil will be the dominant factor in lubrication. Where oil film is not always able to separate the moving metal parts, additives become the dominant factor. The uniform molecular structure of synthetics results in a superior lubricating film. Additionally, the thermal stability of synthetic oils maintains an oil film in much more severe conditions – at higher temperatures, for instance – than petroleum. Additives are relatively equal in performance regardless of the base oil – synthetic or petroleum – with which they are combined. Instead, the anti-wear protection they provide – or fail to provide – is more dependent on their own quality and concentration. For normal temperatures, properly additized petroleum oils and synthetic oils will show similar lubricating qualities. Synthetic oils have higher film strengths and require a lower quantity of additives in order to achieve the same level of protection. In standard anti-wear testing such as the Shell four-ball wear test, some synthetics achieve up to four times the wear protection when compared to petroleum oils. When higher temperatures and pressures are used in such tests, the results significantly favor synthetic oils.

Normal Operational Conditions Advantage: Slightly Synthetics

Severe Operational Conditions Advantage: Very Strongly Synthetics

Oil Life / Endurance

How long can the oil provide proper lubrication and perform all required functions? Oil life is a function of time and severity of service and can vary from vehicle to vehicle. Oil is said to be condemned, that is, not fit for continued service, when one or more of the following conditions exist:

  • Viscosity has decreased by one grade or increased by more than one grade
  • Fuel contamination is greater than three percent
  • Soot level exceeds four percent
  • Total dissolved solids are greater than four percent
  • Total Base Number is less than two
  • Critical additives are depleted
  • Oxidation number greater than 50 (30 for petroleum)
  • Nitration number greater than 50 (30 for Petroleum)

As explained above, synthetic oils are less likely to thicken as the result of vaporization or oxidation and they stay in proper viscosity grade for significantly longer periods of service. Several of the other factors for condemnation are the same for either synthetic or petroleum oils and are more dependent on the quality and concentration of chemical additives required to continue to provide service. Soot and total dissolved solids are products of engine combustion and are proportional to fuel air management; turbo charged engines tend to burn cleaner than naturally aspirated engines. Filtration, especially bypass filtration, will have direct effects on soot and dissolved particles and can be effective at increasing oil life. Since lubricating oils are products of base oils mixed with chemical additives, it becomes painfully obvious that either the failure of the base oil or the depletion of additives will result in condemnation of the oil. Simply put, oils are unique when compared to each other; even if two synthetics are compared, the choice of synthetic base oil and the quality and amount of the additives can produce widely varying finished products.

Oil life is best determined utilizing used oil analysis and then evaluating the remaining oil life based upon the results of a given analysis. Some oil companies, like Mobil and Amsoil, have amassed significant data through oil analysis that enables them to make categorical recommendations for longer drain intervals. It is improper to assume that because you are using synthetic oil, it automatically has an extended drain interval. Some major oil companies – Valvoline is one – are on record as saying their synthetic oil has the same additive package as their petroleum; so, the additives in their synthetic oils deplete just as quickly as their petroleum oils.

Oil Life / Endurance Advantage: Synthetics (varies between synthetic manufacturer)

Petroleum Oil vs. Synthetic Oil: Cost

What is the real cost to use synthetic oil compared to petroleum? To correctly assess cost, it is necessary to differentiate between price and cost. What you pay for an item is the price; how the price is distributed with respect to product utilization over time is cost. For example, if you pay $160 for an 80,000-mile radial tire, then that is the price to purchase the tire. To determine the cost, you have to distribute the $160 over the 80,000 miles; this determines the cost per mile to use the tire. This method allows the direct comparison of products that are priced differently yet have variable life expectancy. Calculating cost is a little of a mixed bag when comparing synthetic and petroleum oils. Not all synthetic oils are designed for extended oil drains, and some petroleum oils will perform much better than others. Comparisons are best done on a case-by-case basis. In general, most any synthetic will run longer between oil drains; however, only a select few are designed for very long drain intervals. For the synthetic oil to be equal or less costly, it must have approximately two to three times the drain interval of a given petroleum oil.

There are other, indirect cost benefits to synthetic oils, including improved fuel economy and superior lubrication that results in less maintenance. One unheralded feature of synthetic oil is insurance; by that, I mean protection from unexpected calamities. The blowing of a radiator hose, the loss of oil or a water pump failure, in most cases, may result in engine damage from excessively high temperatures. When PAO or Ester based synthetics are used, engine damage is highly unlikely to result from engine overheating. This insurance can mean saving thousands of dollars on repairs.

Cost Advantage: Synthetic

Comparing the features of synthetic oils vs. petroleum oils is an exercise that all lubrication professionals have fun with, but, for the consumer, what is the bottom line and what action should you take? Clearly, synthetics win in head-to-head features and benefits, and they also provide intangibles, such as insurance, but should every owner switch? The answer is “no.” If you own an older vehicle with more than 100,000 miles, you should not switch unless you have an experienced professional to guide you through the process. If you have a vehicle with leaks that you cannot fix, then it makes no sense to pour the higher priced synthetic oil on the ground. If, for some reason, your engine is consuming oil at an alarming rate, again, it is not cost-effective to use synthetic oil. On the other hand, synthetic oils are superior in performance; the right synthetic is more cost-effective than petroleum, so there is little reason not to switch. The high temperatures (> 600°F) possible in the turbo-charger make synthetic oils (PAO and/or Ester) clearly the best choice; one failed turbo buys a lot of synthetic oil. If you are towing or otherwise involved in severe duty operations, then synthetics offer so many superior benefits and enhanced protection that it is the only right choice. Using petroleum oil vs. synthetic oil is an option analogous to using bias ply tires instead of radial tires. Of course, the bias ply tire can get you from point A to point B. The difference is in the load carrying capacities, heat range, traction, handling and tread life. For simple, casual driving with no severe conditions, the bias ply tire may work fine, but, in the event of something outside normal conditions, the radial is superior; it is simply a matter of the quality of each tire’s construction.

Petroleum Oil vs. Synthetic Oil: Decision Time

The decision of whether to use petroleum oil vs. synthetic oil is dependent on your unique situation; each of us has his own set of circumstances to assess in order to make a decision based on facts. Understanding the benefits and limitations of engine oil will help you make an informed choice. Making sense of the relationships between oil properties and how those properties protect and preserve an engine is the only real way to analyze true cost effectiveness. Sometimes the decision is obvious; severe duty situations call for synthetic oils. Critical components subject to high temperatures like the turbo-charger are best protected by synthetics. I recommend synthetic engine oils in order to provide the most cost-effective method to achieve the best lubrication possible for your engine.

For questions and/or comments, contact me via my website,, or by email at

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