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Synthetic Oil vs. Conventional: What’s the Difference?

Synthetic motor oil has been around for a while now, but with recent advances in engine technology, more manufacturers are recommending either synthetic or synthetic blends to prolong engine life and improve fuel economy.

What Is Synthetic Oil?

Synthetic lubricants are derived from a number of sources, including completely synthetic compounds, petroleum-based products or other organic oils. Synthetic oil differs from conventional oil because of unique polymers added to the base formulation. This process creates a lubricant that’s better able to withstand high temperature without losing its viscosity, or in layman’s terms, its thickness. There are also so-called synthetic blends that contain no more than a 30 percent conventional oil base. These oils have many of the protective properties of pure synthetic oil but usually cost less.

Which Is Better?

Engine oil is there to protect moving internal parts from damage caused by friction and heat. As such, synthetics are superior to conventional oil because they deliver better lubrication during extreme cold weather and retain their viscosity even after prolonged use. Synthetic oil can also reduce sludge buildup in the oil passages, prolong engine life and improve fuel economy, so while synthetic oil does cost more than conventional oil, it lasts longer, meaning fewer oil changes. In fact, while it is recommended that conventional oil be changed between 5,000- to 7,500-mile intervals, using synthetic oil can extend those numbers to 10,000 miles or more.

We know a quick search of the Internet will expose numerous articles preaching that owners can go 10,000, 15,000 or even 20,000 miles between changes using conventional oil. We don’t recommend pushing your oil-change interval this far, primarily because while oil formulations have improved over the years, oil-filter technology has not. A dirty or clogged oil filter can allow dirt and grime into the oil, and in the long run, can be as damaging to an engine’s life-span as oil that has lost its viscosity. For this reason, we strongly recommend always adhering to the manufacturer’s recommended schedule for oil changes.

Do I Have to Use Synthetic Oil in My New Car?

All cars, even older models, will do better with synthetic oil, but many newer cars actually recommend synthetic oil as part of the car’s regular maintenance. Take, for example, Mazda’s new SKYACTIV engine technology. To achieve maximum fuel economy and power, Mazda’s new-generation engines employ extremely tight tolerance and have high engine-compression ratios. The superiority of synthetic oil is a big part of keeping Mazda’s engines at their peak performance, which is why Mazda specifies 0W-20 engine oil. Note that while Mazda does not say synthetic oil must be used, the engine oil weight of 0W-20, specifically Castrol 0W-20, is only available in synthetic or synthetic-blend formulations. Mazda told Autotrader that customers can use conventional oil with the SKYACTIV engines and it won’t void their warranty, but if you care about protecting your investment, we strongly advise that you follow the manufacturer’s recommendations.

On a larger scale, all General Motors vehicles produced after 2011 are also required to use synthetic oil, and it has to be an oil that meets GM’s own dexos specifications. The new dexos specification was invented by GM, and it basically sets standards that only a synthetic or synthetic-blend oil can meet. You don’t have to use GM’s own ACDelco brand, but you must use a blend that meets the requirements set by GM. There was a bit of controversy when this new policy first debuted in 2012 because customers were led to believe that, if they didn’t use GM’s ACDelco brand dexos oil, their warranty could be void. GM has since clarified its stance, stating that as long as the brand of oil bears the dexos label, it meets the vehicle’s warranty requirements.

The long and short of the synthetic motor oil debate is that, for most vehicles, whether they are V8-powered SUVs or turbocharged 4-cylinder sports cars, the use of synthetic oil is one of the least expensive steps owners can take to prolong their car’s life.


Joe Tralongo
Joe Tralongo
Joe Tralongo is a longtime contributor who started in the industry writing competitive comparison books for a number of manufacturers, before moving on in 2002 to become a freelance automotive journalist. He’s well regarded for his keen eye for detail, as well as his ability to translate complex mechanical terminology into user-friendly explanations. Joe has worked for a number of outlets as... Read More about Joe Tralongo

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  1. Very helpful.  So glad I googled as the Owner’s Manual for my new CX-3 Mazda is as vague as a North Carolina foggy night.

  2. Very helpful.  So glad I googled as the Owner’s Manual for my new CX-3 Mazda is as vague as a North Carolina foggy night.

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