What is the API grade of engine oil?
3 Answers
API engine oil is divided into three categories. The following is the relevant content introduction: 1. The "S" series: Represents oil for gasoline engines, with specifications including: API SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN. 2. The "C" series: Represents oil for diesel engines, with specifications including: API CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, CI-4. 3. When both "S" and "C" letters are present, it indicates that the oil is suitable for both gasoline and diesel engines: The meaning of the letters following S or C is: from "SA" to "SN", each increasing letter indicates that the environmental protection level of the oil is better than the previous one. The further back the letter, the higher the environmental protection level. In international brands, most engine oil levels are above SF, and currently, the highest environmental protection level of engine oil is "SN" grade.
I've been in auto repair for over 20 years. That API symbol on engine oil containers looks quite mysterious, doesn't it? Simply put, it's the 'capability certification' for engine oil set by the American Petroleum Institute. Those starting with 'S' are for gasoline vehicles, and the further the following letter is in the alphabet, the better the performance. For example, the current highest SP grade offers far superior protection compared to SM-grade oil from a decade ago. Those starting with 'C' are for diesel engines, with common grades like CF-4 and CK-4. The key is to check what grade your vehicle's manual specifies. Using SP-grade oil in an old Santana is pure waste, while using SJ-grade in a new turbocharged car might cause cylinder scoring. This grade directly relates to critical performance indicators like detergency, anti-wear properties, and high-temperature stability.
After running an auto repair shop for so many years, I often get asked about the meanings of API and SN/SP on motor oil packaging. Simply put, these represent the oil's 'performance tier'—the higher the grade, the better the performance. Just think about how precise modern car engines are; SP-grade oil offers over 30% better anti-carbon buildup capability compared to the older SN grade. Choosing oil isn't just about price—my old Honda Fit's manual specifies SL-grade oil, so using SP-grade would be a waste of money. But for something like my neighbor's new Camry Hybrid, SP-grade is essential to protect its hybrid system's unique construction. When buying oil, always look for the API donut symbol on the packaging—it's the most reliable indicator.
