What additives are found in engine lubricating oils?
Antioxidants prevent the oil from thickening when it runs hot for extended periods. Detergents help prevent varnish and sludge on engine parts and neutralize acid formed in engine. Pour-point depressants help the oil flow in a cold engine, especially in cold weather. Friction modifiers strengthen the oil film and prevent unlubricated contact between moving parts. Viscosity-index improvers modify the oil so its viscosity is more consistent over a wide temperature range. Dispersants keep contaminants suspended so they don’t form deposits in engine. Rust and corrosion inhibitors protect metal parts from acids and water formed in engine. Foam inhibitors collapse the bubbles churned up by engine crankshaft. (Foam reduces lubricating effectiveness.) Antiwear agents provide lubrication when oil is squeezed out from between moving engine parts. These are all man-made additives that are added to base oil to produce motor oils. These represent by weight 20% of a quart or liter of lubricating oil
