What is SAE 15W40 engine oil?

[Galadriel]

SAE stands for the classification by the Society of Automotive Engineers; 15 represents viscosity, 40 indicates suitable temperature; the symbol W stands for Winter. Below is the relevant introduction to engine oil: 1. Winter oil grades: The winter oil grades under SAE lubricant viscosity classification 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 minimum applicable temperature. 2. Summer oil grades: The summer oil grades under SAE lubricant viscosity classification are: 20, 30, 40, 50. The larger the number, the higher the viscosity and the higher the maximum applicable temperature. 3. All-season oil grades: The all-season oil grades under SAE lubricant viscosity classification 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.