Dry Sump

A dry sump is a lubricating motor oil management method for four-stroke and large two-stroke piston internal combustion engines that uses external pumps and a secondary external reservoir for oil, as compared to a conventional wet sump system.

Four-stroke engines are both lubricated and cooled by oil which is circulated throughout the engine feeding the various bearings and other moving parts of the engine; and thereafter allowed to drain to the sump at the base of the engine under gravity. In most production automobiles, which use a wet sump system, this oil is simply collected in a 3 to 10 litres (0.66 to 2.2 imp gal; 0.79 to 2.6 US gal) capacity pan at the base of the engine, known as the oil sump (or oil pan in American English), where it is circulated back through the engine by an oil pump drawing, or "scavenging" from the sump's reservoir. This pump is mounted internally to the engine and is typically driven by the camshaft. In a dry sump, the oil still falls to the base of the engine, but rather than being allowed to collect in a reservoir style oil sump it falls into a much shallower sump where it is removed by one or more externally mounted scavenge pumps and is pumped into an external reservoir where it is both cooled and deaerated. These pumps are typically belt-driven from the front or back of the crankshaft. Oil is then drawn from this reservoir by the pressure pump and circulated through the engine. Typical dry sump systems have the pressure pump and scavenge pumps mounted on a common shaft so that one pulley at the front of the system can run as many pumps as required by the design of the engine. It is common practice to have one scavenge pump per crankcase section and in the case of a V-type engine an additional scavenge pump to remove oil being fed to the valve gear. Therefore, a V-8 engine would have five scavenge pumps and a pressure pump in the pump "stack".