Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines.  

Motor oils typically consist of base oils enhanced with various additives, particularly antiwear additives, detergents, dispersants, and, for multi-grade oils, viscosity index improvers.

The main function of motor oil is to reduce friction and wear on moving parts and to clean the engine from sludge (one of the functions of dispersants) and varnish (detergents).

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