Microscopic Metallic Particles

Coating metal parts with oil also keeps them from being exposed to oxygen, which inhibits their oxidation at elevated operating temperatures basically preventing them from rusting Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergent additives to help keep the engine clean and minimize oil sludge buildup.Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Sludge also accumulates in the engine. Such particles could circulate in the oil and grind against the moving parts, causing erosion and wear. Because particles inevitably build up in the oil, it is typically circulated through an oil filter to remove harmful particles.
An oil pump, a gear pump powered by the vehicle engine, pumps the oil through the oil filter. Oil filters can be a full flow or bypass type.In the crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journals, bearings, and rods connecting the pistons to the crankshaft. The oil collects in an oil pan at the bottom of the crankcase. In some small engines such as lawn mower engines , dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves.