What does the API index of engine oil mean?

[VonValerie]

API index refers to the grade of engine oil. On the packaging of engine oil, you can frequently see labels such as SN, SM, etc., which represent the API index. The higher the grade, the better the quality of the engine oil. The API classification of oil grades is primarily based on environmental indicators rather than performance indicators. Below is an introduction to the API index: 1. The API (American Petroleum Institute) standard is a widely recognized international standard for lubricating oil quality grades. It uses a two-letter code to indicate the quality level of the oil and the type of engine it is suitable for. The first letter 'S' indicates that it is suitable for spark ignition, i.e., gasoline engines. The first letter 'C' indicates that it is suitable for compression ignition, i.e., diesel engines. The second letter represents performance within different categories, ranging from A, B, C, etc., in ascending alphabetical order. The further the letter is in the alphabet, the higher the grade. 2. Generally, SH-grade oil contains 1300ppm of zinc and 1200ppm of phosphorus. SN-grade oil contains less than 870ppm of zinc and less than 800ppm of phosphorus.