What every driver needs to know about synthetic motor oil

Once used mainly in high-performance vehicles, synthetic oil is now required by most automakers—American, European, and Asian—in some or all of their new cars. Using conventional oil in such vehicles may void your car’s warranty, requiring you to foot the bill for any engine repairs.

There’s good reason for that: Synthetic oil protects engines 47 percent better than conventional oil for all cars—older ones included, according to recent tests by AAA Automotive Engineering. AAA also found that synthetic oil is especially beneficial for vehicles that are used for towing, that operate in extreme climates, or that frequently travel in stop-and-go traffic.

Why is synthetic oil is better?

Engines demand more from their lubricants. The internals of modern engines must be kept clean due to the tight tolerances between their moving parts. If motor oil deteriorates, it can cause a buildup of engine-killing sludge. Because synthetic oil is more chemically stable, it’s less likely to break down than conventional motor oil.

Also, turbocharging—increasing an engine’s power by forcing extra compressed air into its combustion chamber—is now common, and synthetic oil withstands the heat generated by the process.

How does synthetic motor oil differ from regular motor oil?

Synthetic motor oil isn’t made from corn husks, recycled cardboard, or some such thing. According to Mobil, makers of Mobil 1 synthetic oil, both conventional and synthetic motor oil have subterranean origins. Regular motor oil is refined from crude oil, a relatively easy process compared to the manufacture of synthetic oil. The basis for synthetic oil is distilled crude oil; it’s broken down into basic molecules, which are then custom tailored to give specific quality-enhancing properties—designer oil, if you will.

What type of synthetic motor oil should I use?

Automakers have become so picky that some not only require synthetic oil, but a synthetic oil of their own unique blend: “dexos” licensed oils for General Motors cars and “TwinPower Turbo” oil for BMWs are two examples.

The bottom line? You won’t go wrong if you use the motor oil specified in your car’s owners manual. You don’t necessarily have to use an automaker’s brand, but you should use an oil that complies with the automaker’s requirements. If the manual recommends a conventional oil—typical for older cars—you won’t damage the engine by using it. But AAA says it won’t offer the same long-term protection that synthetic oil provides. 

Can an older engine use synthetic motor oil?

Switching to synthetic motor oil is safe with an older engine. The only caveat: If the engine has high mileage or has had infrequent oil changes, you might have to change the oil a couple of times within the first 5,000 miles of switching. That’s because synthetic oil is excels at ridding the engine of built-up deposits and sludge, and the oil will quickly become dirty. After that, you can return to the change intervals prescribed by the automaker.

Some people believe that if you switch to synthetic oil with an older engine, you can never go back to regular oil. That’s one of several myths about synthetic oil, according to the oil company Pennzoil. For more of them, type “Pennzoil synthetic oil myths” into your search engine.

How much does synthetic motor oil cost?

The downside of synthetic oil is that it costs between $2 and $4 dollars more per quart. Because engines typically hold 5 to 8 quarts, that’s as much as $30 or so more per oil change. But that’s a small price to pay if it saves you from costly engine repairs down the road.

Peter Bohr has been writing about cars for more than four decades.