The Difference Between Conventional and Synthetic Oil

We examine the costs and benefits of using synthetic versus conventional lubricants in your car's engine.


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With so many choices available, it's not always easy to know whether conventional or synthetic motor oil is best for your vehicle's engine. How can you discover which oil is the right option for your car? And what are the differences between conventional and synthetic oil?

What is the Difference Between Conventional and Synthetic Oil?

Conventional motor oil is refined from crude oil extracted from the ground. Synthetic motor oil, however, is engineered in a lab.

As a lubricant, traditional oil features molecules of varying sizes, which means its viscosity index (its ability to flow over a range of temperatures) is less reliable. This especially affects performance at high temperatures.

Synthetic oil molecules are designed to have a uniform size, which means their ability to lubricate is stable and reliable at both cold and hot engine temps, flowing more easily throughout an engine and improving its level of protection. It also resists engine heat and stress longer than conventional oil.

Both conventional and synthetic oils contain chemical additives that improve viscosity, function as detergents and help resist corrosion and foaming. It's also possible to purchase a blended oil, combining the two oil types.

How Do I Know Whether My Car Needs Conventional or Synthetic?

The easiest way to tell whether your vehicle requires conventional or synthetic oil is to check the car’s owner's manual. There will be a page (either in the printed or online version) that describes the exact oil type recommended by the manufacturer.

If you own a vehicle that regularly operates in harsh conditions—say, dusty roads, off-road trails, race track driving, heavy-duty towing, extreme summer heat, or extreme winter cold—then you might want to consider using synthetic oil even if it's not required by the manufacturer. Synthetic oil's extra protection and longevity make it easy to recommend under these circumstances, despite the difference in cost.

Is There a Cost Difference Between Conventional and Synthetic Oil?

Modern automobiles increasingly specify the use of synthetic oil, even outside high-performance applications, due to the tighter mechanical tolerances found in newer engines. However, from a budget perspective, synthetic oil's biggest downside is its cost. Typically, synthetics cost twice as much as traditional oil for the same amount of product.

At least the additional expense of synthetic oil is somewhat balanced by the more extended oil change intervals made possible by these lubricants in some vehicles.

Suppose your automobile requires the use of synthetic oil. In that case, you might notice in your owner's manual that oil changes are needed between 7,500 and 10,000 miles during normal driving conditions (or as required by the vehicle's oil life monitoring system). That's in contrast to the shorter recommended change intervals associated with non-synthetic oil. This means you won't need to purchase as much oil over the lifetime of your car or truck, acting as a counterweight to the higher price of synthetic oil.

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Benjamin Hunting
Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.