The following is a detailed introduction to the classification standards for engine oil grades: 1. Types of engine oil: Engine oil grades are divided into gasoline-type, diesel-type, and universal-type (for both gasoline and diesel engines). Those starting with the letter "S" represent oils for gasoline engines, with specifications including API SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN. Those starting with the letter "C" represent oils for diesel engines, with specifications including API CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, CI-4. If both are present, such as SM/CF, it indicates that the oil is universal-type for both gasoline and diesel engines. 2. Meaning of the letters: The further the letter after S or C is in the alphabet, the higher the quality grade of the oil, indicating more stable performance and a higher oil grade. Currently, the market also classifies engine oils into three categories: mineral oil, semi-synthetic oil, and synthetic oil. The corresponding oil grades are SA to SJ for mineral oil, SJ and SL for semi-synthetic oil, and SM and SN for full synthetic oil. In addition to the oil grade identification, some oil packaging may have the SAE label. SAE stands for the Society of Automotive Engineers, which sets the standard viscosity values for engine oils, such as 5W-30. 3. Numerical codes: Numbers like 20, 30, 40, 50 alone indicate summer-use oils, with higher numbers representing higher viscosity and suitability for higher temperatures. Numbers followed by "W" indicate winter-use oils, such as 0W, 5W, 10W, 15W, 20W, 25W. The letter "W" is short for "Winter" in English. The smaller the number before "W," the lower the viscosity, the better the low-temperature fluidity, and the lower the applicable temperature. Codes like 5W-40, 10W-30, 15W-40 indicate all-season oils, suitable for a wide range of temperatures.
