The API (American Petrolium Institute) Engine Oil classification system was setup as a joint effort by API, ASTM (American Society for Testing Materials) and SAE (Society of Automotive Engineers). The API Engine Oil classification are divided into two major categories indicated by the first letter
- The “S” series designation stands for Services Station (or Spark), and is used to
designate products for use in gasoline engines. - The “C” series designation stands for Commercial (or Compression), and is used to
designate oils for use in diesel engines.
the second letter indicates the performance capability of engine oils as defined by series of engine tests that must be passed. Periodically, as more severe engine requirements emerge, new API service classification designation are added proceeding further into alphabet In 1992, changes were introduced to tighten up the API testing procedure. A code of practice was devised by the CMA (Chemical Manufacturers Association) whicj defined a new procedure for the engine testing and evaluation of the lubricant approval according to the API Classification API,SH,CF,CF -2, CF4-, CG4- Classification are now part of the procedure which will provide more consistent proof of performance.the API Classification shouldnot be used as a strict measure of engine oil quality but rather as as guide to its applications.