Which Motor Oil Weight is Right for Your Car?
When choosing motor oil for your vehicle, the first step is always to consult your owner's manual for the manufacturer's recommended oil weight or weights. But what do the different weights stand for?
A typical bottle of motor oil may be labeled "SAE 10W-30." This is often referred to as the oil's "weight," but it actually refers to the oil's viscosity, which is the measure of the oil's resistance to flow. SAE stands for the Society of Automotive Engineers, who created the standards.
So, why two numbers? Oils with two rating numbers like the one shown above are called "multi-grade" oils, and are designed to work for a wide range of temperature conditions. That's why manufacturers almost always recommend multi-grade oils for their vehicles. 5W-30 and 10W-30 are the most common weights for passenger vehicles, and 20W-50 is the most common weight for motorcycles. The number with the "W" refers to the oil's viscosity under cold or "winter" conditions. The other number refers to the oil's viscosity under warm conditions. The lower these numbers, the thinner the oil.
Lower weights can increase the fuel efficiency of your vehicle. In general, lower weights are also used in colder weather, and higher weights are used in hot climates. According to the American Petroleum Institute, here are the most common weights and the lowest expected outdoor temperature when they should be used:
Lowest Expected Temp:
32°F 5W-20, 5W-30, 10W-30, 10W-40, 20W-50
0°F 5W-20, 5W-30, 10W-30, 10W-40
Below 0°F 5W-20, 5W-30
According to this excerpt from the General Motors, the viscosity (weight)used is dictated by the temperature extremes anticipated for the area the vehicle is being driven in.