How is the quality grade of engine oil classified?
2 Answers
Engine oil quality grades are classified according to API standards. API engine oils are divided into two categories: 1. The "S" series represents oils for gasoline engines; 2. The "C" series represents oils for diesel engines. The oil grade levels are classified as SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, and SN. The further the letter is in the alphabet, the higher the grade. Engine oil is a lubricant for engines, consisting of base oil and additives, with base oil being the main component. The functions of engine oil include: 1. Cooling and temperature reduction; 2. Sealing and leak prevention; 3. Cleaning and purification; 4. Shock absorption and buffering; 5. Lubrication to reduce wear; 6. Rust and corrosion prevention; 7. Protection of components.
The quality grade of engine oil is mainly determined by the API certification, which is the standard of the American Petroleum Institute. API grades are represented by letter combinations, such as SP, SN, SM, etc. The 'S' stands for gasoline engines, and the later the letter in the alphabet, the higher the grade. For example, SP is more advanced than SN. Higher-grade oils can better protect the engine at high temperatures, reduce carbon deposits, and offer superior cleaning performance. There's also the SAE viscosity standard, with numbers like 5W-30. The number before the 'W' indicates low-temperature fluidity—the smaller the number, the smoother the cold start. The number after (e.g., 30) represents high-temperature viscosity, suitable for different seasons or vehicle models. When choosing oil for my car, I prioritize the API grade to ensure it meets the manufacturer's recommended standard.
