Q: How do I know what viscosity grade of motor oil is appropriate for my vehicle?
A: Always refer to your vehicle owner’s manual. Oil thins when heated and thickens when cooled. Choosing the proper viscosity grade for the ambient temperature is vitally important. Multigrade oils are the standard year-round choice for drivers who experience hot summers and harsh winters. Multigrades are recognized by the dual viscosity rating (i.e. 10W-30, where the 10W is the low temperature or winter designation and the 30 is the high temperature designation). A viscosity modifier additive produces a thickening effect at high temperatures but is dormant at low temperatures.
General guidelines for multigrade oil: 5W-30 provides excellent fuel economy for temperature conditions below 0° F in most late-model automobiles. 10W-30 is the most frequently recommended motor oil viscosity grade for most automobile engines, best suited for temperatures above 0° F, including high-performance multivalve engines and turbocharged engines. 10W-40, the first multigrade introduced, is a good choice for controlling engine wear and preventing oil breakdown from oxidation in conditions above 0° F —but always check your owner’s manual or warranty requirements before using 10-40. The other multigrades aren’t typical for the average auto. 20W-50, for temps above 20° F, provides maximum protection for high-performance, high-RPMracing engines.SAE30 andSAE40 (above 40° F and above 60° F) are for cars and light trucks, where recommended by manufacturers, but aren’t recommended when cold-temperature starting is required. (Information courtesy Castrol Lubricants)