What is the difference between SN and SM engine oil?
3 Answers
The main difference between SM and SN grade engine oils lies in their viscosity or thickness (phosphorus content) at certain temperatures, with SN grade oil having relatively lower phosphorus content compared to the older SM standard. Below is relevant information about engine oil grades: API (American Petroleum Institute) is the abbreviation for the American Petroleum Association. API grades represent the quality classification of engine oils, using simple codes to describe an oil's performance capabilities. Engine oil grades progress from SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, to SN, with each subsequent letter indicating a higher grade.
I previously researched the difference between SN and SM engine oils. Simply put, SN is newer and more advanced than SM. The SN standard was introduced in 2010, designed for modern vehicles. For example, it provides better anti-wear protection to reduce internal engine wear, controls deposit buildup for smoother engine operation. SM is an older 2004 standard—while it offers decent basic protection, SN upgrades fuel economy to help save gas and reduces phosphorus content to protect catalytic converters from emission issues. If you drive a post-2010 car, manufacturers recommend using SN oil to maintain warranty coverage and performance. I tried switching to SN oil in my older car and noticed more responsive power delivery, plus slightly better highway fuel efficiency. Regularly checking oil specifications matters—don’t cheap out with random low-grade oils, or it’ll impact engine longevity.
I see that SN and SM engine oils mainly differ in environmental friendliness and protection capabilities. SN oil is specifically optimized for newer engines, with stricter emission controls to protect catalytic converters and reduce pollution, while the older SM standard has lower emission requirements, which may lead to increased long-term pollution. When choosing, if your car is relatively new, such as those manufactured after 2010, SN is better; older cars can use SM-compatible oil. I also noticed that SN oil is slightly more expensive, but it saves money in the long run by reducing engine repairs and preventing deposit issues. When maintaining my car, I always check the manual's recommendations—don’t blindly upgrade or downgrade. Keeping the engine clean ensures safer and more comfortable driving.