How are automotive engine oil grades classified?
2 Answers
Automotive engine oils are divided into gasoline engine oils and diesel engine oils. The classification includes two aspects: quality grade and viscosity grade. For passenger cars, in regions like Northeast China, 5W-30 or 5W-40 is recommended, while in southern regions, 10W-40 or 15W-40 is suggested. Here is some relevant information about automotive engine oil: Quality grades of automotive engine oil: In terms of quality grades, the API (American Petroleum Institute) classification includes SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, and SN grades. When selecting engine oil, it is essential to strictly follow the grade specified in the vehicle's user manual. If the same grade is not available, a higher grade can be used, but a lower grade should never be substituted. Impact of engine oil viscosity: The SAE viscosity classification for summer oils includes grades such as 20, 30, 40, and 50. The higher the number, the greater the viscosity, and the higher the maximum applicable temperature.
With 20 years of driving experience, I can tell you that oil grades depend on two key ratings. In the SAE viscosity rating, like 5W-30, the smaller the number before W, the smoother the cold starts, while higher numbers like 30 or 40 after the W indicate better high-temperature protection. Then there's the API classification with letter combinations like SN or SP - it's like smartphone OS updates where later letters mean newer technology. When I changed oil for my old Crown two years ago, I checked the manual: older cars can use SN grade, while newer models need SP-grade to keep up with technology. Some car enthusiasts think more expensive oil is always better, but actually it depends on vehicle age and driving habits - highway commuters and city drivers have completely different requirements.
