Short answer
API SN is a gasoline engine oil category whose first licensing date was October 1, 2010, introduced alongside ILSAC GF-5. API SN Plus was a supplement, first licensed May 1, 2018, that added a test for low-speed pre-ignition (LSPI) in turbocharged direct-injection engines. Both have since been succeeded by API SP (2020) and API SQ (2025).
What API SN covered
API describes SN as improving high-temperature deposit protection for pistons, tightening sludge control and adding seal compatibility requirements compared with API SM. The SN Resource Conserving version matched ILSAC GF-5 and added fuel economy, turbocharger protection, emission-control system compatibility and protection for engines running ethanol blends up to E85.
SN was approved after a long negotiation in which automakers pushed to keep it aligned with GF-5 on items such as phosphorus content, which affects catalytic converters.
Why SN Plus was needed
Within a few years of SN’s launch, small turbocharged direct-injection gasoline engines became common, and automakers began seeing low-speed pre-ignition: fuel and air igniting too early under heavy load at low rpm, sometimes with enough force to damage pistons and rings.
A full new category was still years away, so automakers asked for a faster fix. API added the Ford-developed Sequence IX LSPI test to the SN requirements and called the result SN Plus. It changed little else, which is why it is described as a supplement rather than a new category.
Seeing SN or SN Plus on a bottle today
Oil licensed as SN or SN Plus met those requirements when it was licensed, and some older stock is still on shelves. Plain SN does not include an LSPI test, which matters most for turbocharged direct-injection engines.
If an owner’s manual calls for SN, API’s guidance is that a later category such as SP or SQ in the same viscosity grade includes SN’s performance. The reverse is not true: an SN oil should not be used where the manual calls for SP or newer.
Frequently asked questions
Is SN Plus the same as SP?
No. SP kept an LSPI test like SN Plus but also added a timing chain wear test and updated versions of the oxidation, deposit, sludge and wear tests, so it covers more ground.
My manual says API SN. What should I buy?
An oil in the viscosity grade the manual lists, carrying API SN or a later category such as SP or SQ. If the manual also names an automaker specification, look for that as well.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].