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API Car Engine Oil Specification Explained

The API Specs are a very common sight. You'll find one on almost all engine oil, but what does it all mean?

API (American Petroleum Institute) specifications are often seen on oil containers and they show the minimum standard of oil that can be used in an engine. You can't really use the API specifications to measure the quality of an oil as many of the top end ester based oils meet API SL rather than the latest API SM specification

American Petroleum Institute (API) Engine Oil Specifications

Shop for API Spec Engine Oil / Gearbox Oils

  • S = Service - Petrol Engine Performance
  • C = Commercial - Diesel Engine Performance

Petrol Engine Specification


Introduced November 2004, improved oxidation resistance, deposit protection and wear protection, also better low temperature performance over the life of the oil compared to previous category

Shop For API Petrol SM Spec Engine Oils

Diesel Engine Specification


Introduced 1984, improved control of oil consumption, oil thickening, piston deposits an wear, uses additional multi cylinder test engine.


Introduced 1990, further improvements in control of oil consumption and piston deposits, uses low emission test engine


Introduced 1994, modernised version of CD, reverts to single cylinder low emission test engine. Intended for certain indirect injection engine


Introduced 1994, defines effective control of cylinder deposits and ring face scuffing, intended for 2 stroke diesel engine


Introduced 1994, development of CF4 giving improved control of piston deposits, wear, oxidation stability and soot entrainment. Uses low sulphur diesel fuel in engine test

Shop For API Diesel CG 4 Spec Engine Oils


Introduced 1998, development of CG4, giving further improvements in control of soot related wear and piston deposits, uses more comprehensive engine test program to include low and high sulphur fuels SG - Introduced 1989 has much more active dispersant to combat black sludge.

Shop For API Diesel CH 4 Spec Engine Oils


Introduced 2002, developed to meet 2004 emission standards, may be used where EGR (exhaust gas recirculation) systems are fitted and with fuel containing up to 0.5 % sulphur. May be used where API CD, CE, CF4, CG4 and CH4 oils are specified

Shop For API Diesel CI 4 Spec Engine Oils