Ten Myths About Synthetic Lubricants

It’s a fact of life that behavior is strongly influenced by what people believe, whether true or not. Numerous examples from history bear this out. For example, sailors were once fearful of sailing outside the sight of land less they would fall off the edge of the world. In the early 19th century, the train was considered dangerous because it was believed that if you traveled faster than 25 miles per hour, you would be traveling too fast to breathe. At a later date, the New York Times warned that electric light may cause blindness. Microwave ovens, automobiles and airplanes have had equally vociferous opponents.

Looking back, it is easy to laugh at some of these things people so firmly believed. But these people were not stupid. They were simply misinformed. In many instances they had simply drawn conclusions before all the facts were in. How easy it is to make the same mistake today? In our own time, synthetic motor oils have been the object of many misconceptions held by the general public. Many people, including some mechanics who ought to know better, have been misled by persistent myths that need to be addressed.

The Parameters of the Debate

Synthetic lubricants are fuel efficient, extended life lubricants manufactured from select basestocks and special purpose additives. In contrast to petroleum oils which are pumped from the earth and refined, synthetics are custom-designed in the laboratory, with each phase of their molecular construction programmed to produce, in effect, the ideal lubricant.

In responding to objections most commonly raised against synthetics it is important to establish the parameters of the debate. When speaking of synthetic motor oils, this article is defending the synthetic lubricants which have been formulated to meet the performance standards set by the (API) American Petroleum Institute. (The first such synthetic motor oil to meet these industry-accepted tests for defining engine oil properties and performance characteristics was AMSOIL 100% Synthetic 10W-40 in 1972.)

In an effort to set the record straight, ten of the more persistent myths about synthetic motor oils have been assembled to see how they stack up against the facts.

Myth #1: Synthetic motor oils damage seals.

Untrue. Given that synthetic lubricants are chemically engineered for specific uses, lubricant manufacturers would have no reason not to build their products to be compatible with automotive seals. The composition of seals present problems that both petroleum and synthetic oils must overcome.

Ultimately it is the additive mix in the oil that counts. Additives to control seal swell, shrinkage and hardening are required, whether it be a synthetic or petroleum product that is being produced.

Myth #2: Synthetics are too thin to stay in the engine.

Untrue. In order for a lubricant to be classified in any SAE grade (10W-30, 10W-40, etc) it must meet certain guidelines with regard to viscosity ("thickness").

For example, it makes no difference whether it is 10W-40 petroleum or 10W-40 synthetic, at -25 degrees centigrade (-13F) and 100 degrees centigrade (212 degrees F) must be able to maintain a standardized viscosity or it can’t be rated a 10W-40.

Myth #3: Synthetics cause engines to use more oil.

Untrue. Synthetic motor oils just like petroleum oils are intended to be used in mechanically sound engines, that is, engines that don’t leak. In such engines oil consumption will actually be reduced with the use of synthetics. First, because of the lower volatility of synthetic lubes compared to petroleum based oil. Secondly, because of the greater sealing characteristics between piston rings and cylinder walls. And finally, because of the superior oxidation stability (i.e. resistance of synthetics against reacting with oxygen at high temperatures.)

Myth #4: Synthetic lubricants are not compatible with petroleum.

Untrue. The synthesized hydrocarbons, polyalphaolefins, diesters and other materials that form the base stocks of high quality name brand synthetics are fully compatible with petroleum oils. In the old days, some companies used untested ingredients that were not compatible, causing quality synthetic lubes to suffer a bum rap. Fortunately, those days are long gone.

Compatibility is something to keep in mind, whether using petroleum oils or synthetics. It is usually best to use the same oil for topping off as you have been running in the engine. That is, it is preferable to not mix your oils, even if it is Valvoline or Quaker State you are using. The reason is this: the functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better to use the same oil throughout.

Myth#5: Synthetic lubricants are not readily available.

Untrue. This may have been the case two decades ago when AMSOIL and Mobil1 were the only real choices, but today nearly every major oil company has added a synthetic product to their lines. This in itself is a testament to the value synthetics offer. But, beware, as many of the other products packaged as "synthetics" are not true PAO (Polyalphaolefin) synthetics (ie: Castrol Syntec, Penzoil, etc…) they are hydroisomerized petroleum oil or an ester based synthetic blend. In other words, they are not 100% true synthetic lubes, but synthetics blended with petroleum oils to cut costs.

Myth #6: Synthetic lubricants produce sludge

Untrue. In point of fact, synthetic motor oils are more sludge resistant than their petroleum counterparts, resisting the effects of high temperatures and oxidation. In the presence of high temperatures, two things happen. First, an oil’s lighter ingredients boil off, making the oil thicker. Second, many of the complex chemicals found naturally in petroleum basestocks begin to react with each other, forming sludges, gums and varnishes. One result is a loss of fluidity at low temperatures, slowing the timely flow of oil to the engine for vital engine protection. Further negative effects of thickened oil include the restriction of oil flow to critical areas, greater wear and loss of fuel economy.

Because of their higher flash points, and their ability to withstand evaporation loss and oxidation, synthetics are much more resistant to sludge development.

Two other causes of sludge – ingested dirt and water dilution – can be a problem in any kind of oil, whether petroleum or synthetic. These are problems with the air filtration system and the cooling system respectively, not the oil.

Myth #7: Synthetics can’t be used with catalytic converters or oxygen sensors.

Untrue. There is no difference between synthetic and petroleum oils in regards to these components. Both synthetic and petroleum oils are similar compounds and neither is damaging to catalytic converters or oxygen sensors.

Myth #8: Synthetics void warranties.

Untrue. No major automobile or motorcycle manufacturer specifically bans the use of synthetic lubricants. In point of fact, increasing numbers of high performance cars are arriving on the showroom floors with synthetic motor oils as factory fill.

New vehicle warranties are based upon the use of oils meeting specific API Service Classifications (for example SG/CE). Synthetic lubricants which meet current API Service requirements are perfectly suited for use in any vehicle without affecting the validity of the new car warranty. In point of fact, in the over 25 years that AMSOIL Synthetic Lubricants have been used in extended service situations, over billions of miles of actual driving, these oils have not been faulted once for voiding an automaker’s warranty.

Federal law prohibits a manufacturer from specifying a particular brand of oil be purchased and installed to satisfy warranty requirements.

Myth #9: Synthetic oil is too slippery for use in wet clutches.

Untrue. Many people have the perception that since synthetics are more slippery (reduced friction) than petroleum oils, that wet clutch packs in either automatic transmissions or motorcycle transmissions will slip. Synthetic oils simply have a more uniform molecular structure which reduces frictional resistance better than that of a petroleum oil. Clutch slip is a result of wear and build up on the plates, as opposed to how slippery an oil is.

In fact just the opposite is true. Petroleum oils have a low resistance to heat and allow varnish and glaze to form on clutch plates, which eventually leads to slippage and increased heat generation, thus leading to eventual failure of the clutch pack. Details…

Myth #10: Synthetics are too expensive.

Untrue. Tests and experience have proven that synthetics will greatly extend drain intervals, provide better fuel economy, reduce engine wear and enable vehicles to operate with greater reliability. All these elements combine to make synthetic engine oils more economical than conventional non-synthetics. The following synthetic cost savings article compares synthetic and conventional oils, with a savings of over $50 in just one year.

This proves that synthetic lubricants are actually more economical than conventional petroleum based oils.

In Europe, synthetics have enjoyed increasing acceptance as consumers look first for performance and long term value rather than initial price. As greater demands are placed on the world’s petroleum supplies and the superior benefits of synthetics are realized, we will no doubt see an increasing re-evaluation of oil buying habits in this country as well.


Since their inception, manufacturers of synthetic motor oils have sought to educate the public about the facts regarding synthetics, and the need for consumers to make their lubrication purchasing decisions based on quality rather than price. As was the case with microwave ovens or electric lights, a highly technological improvement must often overcome a fair amount of public skepticism and consumer inertia before it is embraced by the general population.

But the word is getting out as a growing number of motorists worldwide experience the benefits of synthetic lubrication. The wave of the future, in auto lubes, is well under way.

Portions of this article were first published in National Oil and Lube News by Ed Newman