Synthetic Oil Versus Regular Oil

There is a lot of buzz and confusion about synthetic motor oil. In fact, you may be wondering: why is it called "synthetic"? Is it better for my car then conventional oil? Is it safe for my car? Does it last longer? Can synthetic oil be mixed with regular oil? Here is an attempt to answer these questions.

Regular Oil

Regular oil is made by refining crude oil pumped from the ground. This involves heating the oil via a distillation process that separates out the long-chain oil hydrocarbons from the other hydrocarbons such as those used to produce gasoline and diesel fuel. Following distillation, the oil is further purified to produce a "base stock" to which specially formulated additives are applied to improve the oil's lubrication properties such as anti-wear, anti-foam, oxidation resistance, detergency, and viscosity.

Synthetic Oil

Synthetic oil is derived from refined crude oil that is further modified and purified to produce a higher level base stock. Other raw materials such as methane, carbon monoxide, and carbon dioxide may also be used. The oil is termed synthetic because these natural ingredients are chemically recombined to yield synthesized-hydrocarbon molecular chains of more consistent size and shape than those found in even the highest-quality conventional motor oil. The result is a lubricant with enhanced film strength that is better able to withstand extreme engine temperatures. By contrast, regular oil can easily vaporize or oxidize in conditions of extreme heat. As with regular oil, additives are added to synthetic oil to further improve its lubricating properties.

Synthetic oils were developed by both Germany and United States in the 1940s for lubricating aircraft engines. In 1972, AMSOIL introduced the first synthetic motor oil for automobiles. Although they were slow to catch on, all of the major oil companies added synthetic oils to their product lines by the 1990s.

Oil Change Interval

Synthetic or synthetic blended oils are not really designed to extend oil change intervals beyond the manufacturer recommendation. That being said, it is not uncommon to go 5000 to 7500 miles between changes with synthetic oil versus 3000 to 4000 miles for regular oil. Some manufacturers, such as Toyota, actually prescribe a change interval of 10K miles for many of their newer vehicles. Some people push the synthetic oil change interval even higher but that's not a good idea as harmful deposits still build up in the oil over time even though it may retain its lubricating qualities.


Synthetic oil typically costs twice as much as conventional oil. However, because it lasts longer, allowing for longer change intervals, it could be argued that the price premium is more like 50 to 60%.

Best Oil For Your Car

Synthetic oil would seem to have the edge over regular motor oil. It offers reduced engine wear, easier startups at cold temperatures due to better flow characteristics ( less viscosity), greater viscosity at high temperatures, more resistance to viscosity breakdown, reduced engine deposits and contaminants, and improved gas mileage.

Synthetic oils have improved greatly over the last 20 years and are safe to use in most vehicles, especially newer ones. On older, high mileage vehicles, full synthetic oil may not be the best choice because it could result in internal oil combustion because it is so thin and free-flowing.

Because synthetic oil costs considerably more than regular oil, a strong case could be made for sticking with regular oil assuming that the oil is changed per the manufacturer's recommended interval and the vehicle is not routinely subjected to the extreme operating conditions that warrant the additional engine protection of synthetic oil.

Switching Between Synthetic and Regular Oil

Synthetic and conventional oils are compatible with each other so mixing the two or switching back and forth between them will not cause problems.