What Do the Numbers on Engine Oil Mean?
2 Answers
Automotive engine oil labeling uses the viscosity classification method established by the Society of Automotive Engineers (SAE). This is a viscosity grading system that divides lubricants into high-temperature types for summer use, low-temperature types for winter use, and all-season types suitable for both winter and summer. The specific meanings are as follows: 1. Winter oil grades are: 0W, 5W, 10W, 15W, 20W, 25W. The symbol W stands for Winter, and the smaller the number before W, the lower the low-temperature viscosity, the better the low-temperature fluidity, and the lower the applicable minimum temperature. 2. Summer oil grades are: 20, 30, 40, 50. The larger the number, the higher the viscosity and the higher the applicable maximum temperature. 3. All-season oil grades are: 5W/20, 5W/30, 5W/40, 5W/50, 10W/20, 10W/30, 10W/40, 10W/50, 15W/20, 15W/30, 15W/40, 15W/50, 20W/20, 20W/30, 20W/40, 20W/50. The smaller the number representing the winter part, and the larger the number representing the summer part, the higher the viscosity and the wider the applicable temperature range.
I've been driving for over twenty years, and the oil viscosity ratings are pretty straightforward. The number before the W indicates cold-weather fluidity—for example, 5W means the oil won't be too thick when starting the engine in cold weather, allowing it to flow quickly to all parts of the engine. The number after the W, like 30, represents viscosity at high temperatures. The higher this number, the thicker the oil is in hot weather or during highway driving, providing better protection. But don’t assume higher numbers are always better—my old American car’s manual recommends 10W-40, but switching to 5W-30 actually improved acceleration because thinner oil has less resistance. Also, full synthetic oils perform better in low temperatures, so using a 0W oil in northern winters is especially hassle-free.
