An oil filter is a device used to decontaminate oil that contains suspended impurities. A major application is in forming part of the lubrication system of engines in which filters are typically detachable units due to the need for regular service or replacement. The filtration of oil in engines is essential for enhancing longevity and performance.

In engines, there is inevitably some exposure of the oil to products of internal combustion, and microscopic coke particles from black soot accumulate in the oil during operation.

For these reasons, the oil and the oil filter need to be periodically replaced.

Engine oil is a type of liquid oil used for lubrication by various types of internal combustion engines. While the main function is to lubricate moving parts, motor oil also cleans, inhibits corrosion, and cools the engine by carrying heat away from the moving parts.

In engines, there is inevitably some exposure of the oil to products of internal combustion, and microscopic coke particles from black soot accumulate in the oil during operation. Also the rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against the part surfaces causing erosion and wear. The oil filter removes many of the particles, but eventually the oil filter becomes clogged. The motor oil and especially the additives also undergo thermal and mechanical degradation.

For these reasons, the oil and the oil filter need to be periodically replaced.