API oil standards explained: what SN, SP and CK-4 mean
A viscosity grade like 5W-30 only tells you how easily an oil flows. Its quality and performance level is shown by the API category — the two letters on the label.
What is API?
The American Petroleum Institute classifies engine oils by standardised tests. An oil that passes them may carry the matching service category on its label.
First letter: engine type
- S (Spark) is for petrol and gas engines.
- C (Compression) is for diesel engines.
Second letter: quality level
The further along the alphabet, the newer and stricter the standard. For petrol engines the sequence is SJ, SL, SM, SN and then SP. SP is the current top level, with better protection against deposits, timing-chain wear and low-speed pre-ignition (LSPI) in turbocharged direct-injection engines.
For diesels, CF, CH-4, CI-4 and CK-4 are common. CK-4 is designed for modern engines with diesel particulate filters (DPF) and EGR, and produces less ash.
Is a higher standard always better?
Newer categories are generally backward compatible: an SP oil can be used where SL is specified. The reverse is not true — an SL oil is not enough for an engine that requires SP. The minimum standard in your owner’s manual is what counts.
What about ACEA and ILSAC?
ACEA is the European standard (such as A3/B4 or C3) and matters for European cars. ACEA C categories are low-SAPS oils that protect particulate filters and catalysts. ILSAC (such as GF-6) focuses on fuel economy and is common for Asian and American cars.
Quick answers
Which API level do most cars need?
Can I use SP oil in an older engine?
What is the difference between CK-4 and CI-4?
See our passenger car engine oils range, or ask our sales team for a recommendation and price.
