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Motor Oil Myths

Separating facts about friction

Misunderstanding, misinterpretation, and some downright myths surround motor oil. This is largely because motor oil is an extremely complex, heavily researched, continuously improved and extensively tested product. However, it all looks, feels, smells and, we assume, tastes pretty much the same. While most humans can’t tell the difference, engines can.

Little has created more motor oil misunderstanding than synthetic oil. One reason: Unless you’re currently receiving an “A” in Advanced Placement Chemistry, the concept of making motor oil from something that is not oil is difficult to grasp.

Also, synthetic oil has radically evolved since it was first mass-produced during World War II by Germany, which had little petroleum but plenty of coal and methane gas. Soon after the war, chemists found that they could use other source material—such as ethylene gas—to create oil that would better survive the rigors of jet aircraft engines than that refined from crude oil. Called polyalphaolifin or PAO, these synthetics perform better in extreme conditions because chemists can design the oil molecules for the specific task and make all the molecules uniform. (Sign up for AP Chem if you want more.)

Synthetic oil can be made—synthesized—from many sources, including crude oil. If you see a couple guys in white lab coats wrestling on the ground, they’re probably oil-company chemists arguing the pros and cons of crude-oil-based synthetics versus PAO synthetics.

Here are some of motor oil fallacies that may, or may not, have been true in 1942 or 1982, along with the current truth.

Fallacy

It’s bad for my engine to switch between synthetic and conventional motor oil.

Truth

Today’s synthetics are totally compatible with conventional oil, and other leading synthetics. Switch back and forth all you want. Some who live where temperatures plummet well below zero use synthetic in the winter for its protection during cold starts and extreme temperatures and then switch to lower-priced conventional oil for warmer weather.

Fallacy

Synthetics are bad for engine seals.

Truth

Today’s synthetics are designed to play nice with all engine seals. While 30 years ago some synthetics reacted differently with some engine seals than did conventional motor oil, chemists for oil companies long ago cured that issue.

Fallacy

For the average motorist, synthetic has no significant advantage over conventional motor oils.

Truth

The top attribute of synthetic motor oil is its superiority in extreme conditions and one of the most severe is a “cold start”. Anything under 160 degrees or so is chilly to an engine.

Fallacy

Conventional motor oil is a natural and unprocessed product, while synthetic is made in a laboratory.

Truth

Both conventional and synthetic motor oils go through elaborate production processes: Oil straight from the ground would quickly ruin your engine. Base sources for synthetic oil are just as “natural” as is crude oil—and might even be crude oil.

Fallacy

Synthetic—or any other—oil can significantly improve horsepower.

Truth

Well this one really depends on you interpret the question and how you define significant. Let’s first look at whether or not switching from one oil to another can immediately give you more horsepower; for a race driver where a few tenths of a percent extra horsepower can be the difference between 1st and 5th the answer is yes but for a regular driver even one towing a loaded trailer uphill, the answer is no. Formulators can modify the frictional characteristics of an oil to allow more of the engine’s power to end up at the wheels, but these differences are too small to be seen in normal operation.

Now, lets look at this a little differently, “Can using one oil versus another for an extended period have an impact on the power output of my engine?” Here the answer is yes, using low-quality oil will result in increased engine wear and increased engine deposits and over time this will result in a loss in engine efficiency and power. Use of high-quality oil will minimize wear and deposits and any resulting efficiency or power losses as the engine ages.

Fallacy

Synthetic oils are too thin for older cars and will cause a high-mileage car to use more oil. Older cars must use conventional motor oils.

Truth

Especially for those specifically formulated for higher-mileage engines, today’s synthetics work just fine in older cars. Synthetic is no more prone to leaking than conventional oil. This fallacy might have been created by some synthetics from the early ‘80s.

Fallacy

Synthetics create more sludge.

Truth

Synthetics create less sludge: That’s one reason jet-engine makers liked them 60 years ago. Speculation says that this fallacy was created when people switched a vehicle with a poor oil-change history to synthetic. While synthetic may loosen built-up sludge, a change using conventional oil probably will do something similar with a poorly maintained vehicle. When facing such a situation, change the oil filter after about 750 miles and cut it apart to see if it’s filled with sludge.

One more truth: Motor oil is the most important—but the least understood and appreciated—fluid you put in your car.