What does engine oil API mean?
3 Answers
Engine oil API refers to the American Petroleum Institute. The API grade of engine oil is the quality standard set by the API for engine oils. The first letter of the specification for engine oils used in gasoline engines is 'S', while for diesel engines, it is 'C'. Engine oil, also known as motor lubricant, serves to lubricate and reduce friction in the engine, assist in cooling, seal against leaks, prevent rust and corrosion, and provide shock absorption. Engine oil consists of two parts: base oil and additives. The base oil is the main component of the lubricant, determining its basic properties, while additives compensate for and improve the shortcomings of the base oil, imparting new properties and making them an essential part of the lubricant.
The API (American Petroleum Institute) rating is a standard code for engine oil, such as the SP or SN letters printed on the bottle. This rating represents the comprehensive performance level of the oil, with later letters indicating more advanced formulations. For example, the current mainstream SP grade offers additional protection against low-speed pre-ignition compared to the older SN grade, making it more suitable for turbocharged direct-injection engines. During my repair work, I've encountered numerous cases of incorrect API grade selection—some people used outdated SJ-grade oil in new cars, resulting in sludge clogging the oil passages after just 5,000 kilometers, requiring an 8,000+ RMB overhaul. I strongly recommend checking your vehicle manual for the specified API requirement rather than choosing oil based solely on price.
Once when I was servicing my old Camry, I noticed the engine noise was unusually loud. The auto repair shop owner checked it and said I had used the wrong API grade of engine oil. Turns out I had been casually buying SL-grade oil, but the manual required SM-grade or higher. He explained that API is like an ID number for oil, with SM having better heavy metal control and anti-oxidation formulas than SL. After switching to SN-grade oil, the engine immediately quieted down. Now I always look for the SP symbol on oil cans, and even after 7,000 kilometers, the new oil remains crystal clear. When changing oil regularly, remember to check the API letters—don't make the same mistake I did initially.
