What does 5W in engine oil mean?

[Ralph]

Engine oil 5W represents the low-temperature fluidity of the oil as 5W. W stands for Winter; the smaller the number before W, the better the low-temperature fluidity of the oil, and the lower the ambient temperature it can be used in. Here is some introduction to engine oil: 1. Engine oil classification: There are two types, one for gasoline engines and the other for diesel engines. Oils starting with S are for gasoline engines, with quality levels ranging from SA to SN, totaling 12 types; oils starting with C are for diesel engines, with levels including CA, CB, CC, CD, CE, CF, etc. 2. Engine oil viscosity specifications: Different types of oil have their own viscosity specifications. Taking 5W30 oil as an example, 5 represents the cold start performance of the oil, the smaller the number, the stronger the oil's cold resistance; 30 represents the kinematic viscosity standard at 100 degrees Celsius.