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What is the Difference Between SL and SN Engine Oil?

2 Answers

DiDawson

07/25/25 12:32pm

The most obvious difference lies in the performance grade: In engine oil labeling, SL refers to the oil's grade. API (American Petroleum Institute) is the abbreviation for the American Petroleum Institute, and the API grade represents the quality level of engine oil. It uses simple codes to describe the working capability of engine oil. Engine oil grades range from SA to SN, with each subsequent letter indicating a higher grade. Currently, the most common grades are SL, SM, and SN. Relevant information: 1. Difference in oxidation resistance and anti-wear performance: The same TEOST-MHT high-temperature deposit test shows that SN's requirement is no more than 35 milligrams; SN's high-temperature detergency is higher than SL's, making it especially suitable for turbocharged engines; SN-grade oil has higher oxidation stability and anti-wear properties. Since SN oil contains lower levels of phosphorus and zinc compared to SL oil, it reduces wear on the three-way catalytic converter. 2. Different environmental protection levels: Engine oils are categorized by environmental protection levels, with higher letters indicating better environmental performance. Therefore, "SL" oil has a lower environmental protection level than "SN," and the highest environmental protection level is "SN" grade. 3. By quality level: SG, SH, SJ, SL, SM, SN, so SN's quality is higher than SL's.

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StCarmen

08/11/25 8:22pm

As a truck driver with decades of experience, I still remember using SL-grade oil in my younger days. The switch to SN-grade represents significant progress, primarily in environmental protection—SN reduces phosphorus content, offering better protection for the catalytic converter in the exhaust system, unlike SL which is more prone to clogging or air pollution. In terms of performance, SN improves oxidation resistance, reducing engine sludge buildup and ensuring smoother operation. I’ve also noticed that vehicles using SN oil consume slightly less fuel, saving on maintenance costs in the long run. However, for older cars originally recommended for SL, switching to SN is still acceptable, as long as the vehicle isn’t too outdated. I advise drivers to pay attention to the API certification on oil bottles to avoid unnecessary issues. Don’t delay oil changes, and regular engine checks are crucial.

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