Choosing the right oil used to be difficult. Thick oils were recommended for summer service and thin oils were recommended for winter service. For extremely hot summers or cold winters, relatively thicker or thinner oils were required. Modern multiviscosity (multigrade) oils and the domestic and Japanese automakers have made the choice a lot easier. Now, the only grades recommended for domestic and Japanese and modern engines are 5W-30 and 10W-30. Only special applications like racing, very severe driving conditions or older cars require an alternate viscosity grade.

The following chart matches motor-oil viscosity grades to expected temperature ranges before your next oil change. But your owner's manual is always the best guide to the proper viscosity grade.