motor oil

Pouring fresh motor oil into an engine Quart containers of branded bottled motor oil at a store

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). It also neutralizes acids that originate from fuel and from oxidation of the lubricant (detergents), improves the sealing of piston rings, and cools the engine by carrying heat away from moving parts.