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Choosing the Right Engine Oil

By Mike Hanley, Cars.com
Many owner's manuals explain which conditions are best for different motor oil viscosities.

If you want to own and properly maintain a vehicle, at some point you'll have to figure out what kind of oil your car takes. Whether you're at a service center being asked what kind of oil you want or at a parts store shopping for oil to top off the engine, you'll want to know what's recommended.

The owner's manual gives all the information necessary to put the right viscosity oil — 10W-30, 5W-30, etc. — into your car. Most will have a temperature chart showing which conditions are best for different viscosities. It's also common to see the recommended oil printed on the oil cap under the hood.

It's also important to use oil that meets the automaker's standards, which commonly includes oil with an American Petroleum Institute certification. API-certified oil will have the organization's "starburst" logo printed on the oil container, signifying the oil meets the most up-to-date oil-performance standards.

What Do All Those Numbers Mean?

Make sure the new oil meets the manufacturer's recommendations. Make sure the new oil meets the manufacturer's recommendations.

The seemingly cryptic 5W-30 and 10W-30 designations represent the viscosity, or thickness, of engine oil. Which thickness of oil works best in your engine is determined by the automaker. Some common viscosities used in modern cars are 5W-30, 10W-30, 5W-20, 0W-30 and 5W-40.

The numbers represent oil thickness as measured by the Society of Automotive Engineers during hot and cold testing. For 10W-30, the first number (10) is the oil's viscosity when cold; 10 weight is thinner than 30 weight and beneficial when cold, because thinner engine oil allows easy start-up and less strain on the engine. The second number (30) is the oil's viscosity when warm and is typically a heavier oil, to provide better protection at higher temperatures.

The "W" paired with the first viscosity (10W) designates an oil that is certified by SAE for low-temperature use in winter.

Should I Use Synthetic Oil?

Synthetic oils are man-made oils that handle extreme hot and cold temperatures better than conventional, natural oils. Natural oils break down faster during high-heat operation like towing, racing or any heavy-load operation, partly because of impurities that can't be removed in the refining process.

As you would expect, synthetic oil is more expensive than conventional oil. Some synthetic oils claim you can change your oil less frequently when using their oil, but many automakers recommend sticking to their original oil-change timelines even when using synthetic.

Some new cars come with synthetic oil straight from the factory, and some automakers have vehicles that recommend synthetic oil.

Will Using the Wrong Oil Void My Warranty?

If you don't use the recommended oil viscosity or approved oil as required by the automaker, you risk voiding your warranty if damage occurs because of using the wrong oil. Other ways to void a warranty include using a heavy oil weight, like 20W-50, in a car that recommends 5W-30, or using non-API-approved oil in a car requiring API certification. One more way to void a warranty is to use synthetic oil that's not approved by the automaker.


© Cars.com 04/30/2013