How is the quality grade of gasoline engine oil classified?
2 Answers
API grades represent the quality levels of engine oil. Here are the relevant details: 1. API engine oils are divided into two categories: the 'S' series represents oils for gasoline engines, and the 'C' series represents oils for diesel engines. 2. The oil grade levels are classified as: SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, and SN. The later the letter in the alphabet, the higher the grade, with SN being the highest grade oil currently available. 3. The 'C' series represents oils for diesel engines, with specifications including: API CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, and CI-4.
I've been repairing cars for over 20 years and witnessed how oil grades are determined. It's mainly based on API classifications, evolving from SA to SB and now to SP. SP represents the latest high-performance oil specifically designed to address low-speed pre-ignition issues in new engines. The classification follows API testing standards: 'S' prefix denotes gasoline engine oils, and alphanumeric combinations like SN offer better protection than SM, while SM has superior oxidation resistance. Why does it matter? Older cars can use SM, but newer turbocharged engines require SP for proper protection - otherwise, rapid carbon buildup occurs. Relatedly, oil must match SAE viscosity grades - never choose the wrong oil arbitrarily. Stick to regular oil change intervals to save significant repair costs. Always check your manual's recommended grade during maintenance - I've seen too many owners regret engine overhauls after using lower-grade oils improperly.
