SAE and API

The lubrication oils are normally classified according to their viscosity. The SAE (Society of Automotive Engineers) method of assigning numbers to different oils is in universal use.


















SAE has assigned a number to an oil whose viscosity at given temperatures falls in certain range. SAE 5W, 10W and 20W grades are defined in term of viscosity at -18C and are oils which render starting in cold climates easy, while SAE 20, 30, 40 and 50 grades defined in term of viscosity of 99C (210F), are the oils which work satisfactory in normal and hot climates.


Since SAE grades are based solely on viscosity they do not bear any relationship to oil quality. Addition of certain additive can materially influence their performance under different operating conditions and different characteristics of oil burnt.

Therefore API (American Petroleum Institute) adopted in 1947 a system which divided a crank-case oil into three classes, regular type, premium type and heavy duty type, depending upon the properties of oil and the operating conditions under which it was intended to be used.

Generally regular type oils were stright mineral oils, premium type contained oxidation inhibitors and heavy type contained oxidation inhibitors plus detergent dispresent additives.


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