Wet sump

A wet sump is a lubricating oil management design for four-stroke piston internal combustion engines which uses a built-in reservoir for oil, as opposed to an external or secondary reservoir used in a dry sump design.

Four-stroke engines are lubricated by oil which is pumped into various bearings and thereafter allowed to drain to the base of the engine. In most production cars and motorcycles, which use a wet sump system, the oil is collected in a three to seven quart (3 to 7 L) capacity pan at the base of the engine, known as the oil pan or sump where it is pumped back up to the bearings by the oil pump, internal to the engine.

A wet sump offers the advantage of a simple design, using a single pump and no external reservoir. Since the sump is internal, there is no need for hoses or tubes connecting the engine to an external sump which may leak. An internal oil pump is generally more difficult to replace, but that is dependent on the engine design.

However, the wet sump design is entirely unsuitable for a racing application, for example, as the large g force pulled by drivers going around corners causes the oil in the pan to slosh, starving the system of oil for a small period of time. This can damage the engine.

Early stationary engines employed a small scoop on the extremity of the crankshaft or connecting rod to assist with the lubrication of the cylinder walls by means of a splashing action. Modern small engines, such as those used in lawnmowers, use a "slinger" (basically a paddle wheel) to perform the same function.

See also