When we set out to bust some of the myths behind synthetic oil, we received some surprising responses, mostly from those in the industry. They called it a political hot potato to glean too much from their vast websites and information centers, and we weren't prepared to do any scientific testing of our own. But we trudged ahead anyways and discovered that people have lots of misconceptions about synthetic and even petroleum oil products. So many, in fact, that we couldn't resist releasing some of their findings.
One person who was glad to shed some light on the subject was Ed Newman of Amsoil. He let us peer into his world so that we could better understand the truth behind the myth. "Looking back, it's easy to laugh at some of the things people so firmly believed," said Newman. "These people were not stupid. They were simply misinformed. In many instances they had simply drawn conclusions before all the facts were in."
In our own time, motor oils, and in particular synthetic ones, have been the object of numerous misconceptions held by the general public. Many people, including mechanics who ought to know better, have been misled by persistent myths that need to be addressed.
Myth 1: You will damage your seals by using synthetic oils.
It would be foolhardy for lubricant manufacturers to build a product that is incompatible with seals. The composition of seals presents problems that both petroleum oils and synthetics must overcome. Made from elastomers, seals are inherently difficult to standardize.
Ultimately it is the additive mix in oil that counts. Additives are required to control seal swell, shrinkage, and hardening, whether the oil product is synthetic or petroleum.
Myth 2: Synthetics are too thin to stay in the engine.
In order for a lubricant to be classified in any SAE grade (10W-30, 10W-40, and so on) it has to meet certain guidelines with regard to viscosity (thickness). For example, it makes no difference whether it's 10W-40 petroleum or 10W-40 synthetic; between minus 25 degrees C (minus 13 F) and 100 degrees C (212 degrees F), the oil has to maintain a standardized viscosity or it can't be rated a 10W-40.
Myth 3: Synthetics cause you to use more motor oil.
Synthetic motor oils are intended for use in mechanically sound engines; that is, engines that don't leak. In such engines, oil consumption will actually be reduced, first because of the lower volatility of synthetics, second because of the better sealing characteristics between piston rings and cylinder walls, and finally because of the superior oxidation stability (i.e., resistance of synthetics to reacting with oxygen at high temperatures).
Myth 4: Synthetic lubricants are not compatible with petroleum.
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. Compatibility is something to keep in mind, however, whether you're using petroleum oils or synthetics. It is usually best to use the same oil for topping off that you have been running in the engine. That is, it is better not to 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.