What is the shelf life of motor oil after opening?

[DiJoanna]

Motor oil has a shelf life of 6 to 9 months after opening. Motor oil, engine oil, or engine lubricant is a substance enhanced with additives in base oil, mainly containing anti-wear additives, detergents, dispersants, and multi-grade oil viscosity index improvers. Motor oil is used for lubricating internal combustion engines. Its primary functions are to reduce friction and wear on moving parts, and to remove sludge (one of the functions of dispersants) and varnish (function of detergents) from the engine. Motor oil is the lubricant used in internal combustion engines that power cars, motorcycles, lawn mowers, internal combustion engine generators, and many other machines. In an engine, some components move relative to each other. Friction converts kinetic energy into heat energy, wasting useful power and wearing down these parts, which can lead to reduced engine efficiency and degradation. This increases fuel consumption, reduces power output, and may cause engine failure.