What does engine oil API mean?

[OAubrey]

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.

[AlinaDella]

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 During my repair work, I've encountered numerous cases of incorrect API grade selection—some people used outdated SJ-grade oil in new cars, resulting in sludge clogging the oil passages after just 5,000 kilometers, requiring an 8,000+ RMB overhaul.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.

[Carol]

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.

[SanDallas]

When teaching my daughter how to choose engine oil, I used an analogy: The API rating is like the diploma of engine oil. The American Petroleum Institute grades engine oils, where SP is equivalent to a Ph.D., SN is a master's degree, and SJ is a high school diploma. Your new SUV needs the Ph.D.-level SP grade to perform well; using lower-grade oil is like asking a high school student to repair a rocket. From my own experience, cars from this century should use at least SM grade or higher, otherwise, sludge can easily form. Nowadays, most auto repair shops stock SP-grade oil on their shelves. I recommend checking the manual for the corresponding grade before changing the oil.

[OJayden]

When I first started researching cars, I also didn't understand the API symbol on motor oil bottles. Later, I learned through research that this standard dates back to 1930, originally classifying diesel grades like CA/CB. Gasoline engine oils started with SA and have been upgraded to the current SP level. Each upgrade addresses new issues, such as the SM level in 2004 targeting emission standards, and the SN level in 2010 enhancing turbo protection. Older cars can use SJ grade without issues, but new cars after 2018 generally require SP. My advice is to choose oil based on the production date - for cars made in the last five years, buying SP grade is definitely the right choice.

[McRuby]

Last week, when changing the oil for a customer's BMW, the work order specifically noted that API SP-grade oil must be used. Upon testing the old oil, I found it didn't meet the API grade—only SM-grade—which led to sludge clogging the VVT valve. Professional technicians know that the API grade determines the additive formulation, with SP-grade containing more detergents, dispersants, and anti-wear agents. When selecting oil, pay attention to three key points: check the manual for the required grade, match the production date to the corresponding standard, and avoid unverified bulk oils. Especially for turbocharged vehicles, using lower-grade oil may cause piston ring seizure.