Dry sump
![Schematic diagram of a basic dry sump engine lubrication system. Engine lubricating oil collects in sump (1), is withdrawn continuously by scavenge pump (2) and travels to the reservoir (3), where gases entrained in the oil separate and the oil cools. Gases (6) are returned to the engine sump. Pressure pump (4) forces the de-gassed and cooled oil (5) back to the engine cylinder head (7).](/Images/godic/202501/10/Dry_sump.svg2505.png")
A dry sump is a lubricating motor oil management method for four-stroke and large two-stroke piston internal combustion engines that uses additional pumps and a secondary reservoir for oil, as compared to a conventional wet sump system, which uses only the main sump (U.S.: oil pan) below the engine and a single pump. A dry sump can also be implemented with a single vacuum pump that creates positive and negative pressures to pull and push the oil out and into the engine. A dry sump engine requires a pressure relief valve to regulate negative pressure inside the engine, so internal seals are not inverted.