Oil cooling uses engine oil as a coolant and is typically used to remove excess heat from the internal combustion engine. The hot engine transfers heat to the oil, which then passes through a heat exchanger, usually a heat sink called an oil cooler. The cooled oil flows back into the hot object for continued cooling.
Oil cooling is commonly used to cool non-liquid cooled high performance motorcycle engines. Typically, the cylinder bore maintains air cooling in a conventional motorcycle mode, but the cylinder head benefits from additional cooling. Since there is already an oil circulation system available for lubrication, this oil is also piped to the cylinder head and used as a liquid coolant. Compared to oil systems used only for lubrication, oil cooling requires additional oil capacity, greater flow through the oil pump, and oil cooler (or cooler than normal).
If air cooling proves to be sufficiently large (such as an aeronautical engine in flight or a motorcycle in motion), then oil cooling is an ideal way to deal with those times when additional cooling is required (eg aero engines before takeoff, or urban traffic jams) Motorcycles in. But if the engine is a racing engine that always produces a lot of heat, water or liquid cooling may be preferred.
Air-cooled aero engines may experience "shock cooling" when descending from cruising altitude before landing. During the descent, very little power is required, so the engine is throttled back, so much less heat is generated than when the height is maintained. When descending, the airspeed of the aircraft rises, greatly improving the air cooling rate of the engine. These factors can cause the cylinder head to rupture; however, the use of oil-cooled cylinder heads can significantly reduce or eliminate problems because these heads are now "oily."
In the 1980s, Suzuki used the "SACS" oil-cooling system on the GSX-R sportbikes, but later switched to water-cooling.
The Wankel engine features oil cooling in addition to liquid-cooling to successfully manage its excessive heat. This rotary engine is most famous for its application in the Mazda RX-7 and RX-8.
Splash lubrication is a rudimentary form of oil cooling. Some slow-turning early engines would have a "splashing spoon" beneath the big end of the connecting rod. This spoon would dip into sump oil and would hurl oil about, in the hope of cooling and lubricating the underside of the piston.