An Oil Cooler is a system for diverting engine oil outside of the engine to a radiator for cooling purposes. Most automatic transmissions are equipped with an oil cooler that's located inside the radiator.

Since the radiator usually runs close to 200 degrees, the amount of "cooling" this kind of setup provides is important. A good quality oil cooler that can be installed outside the radiator provides much better cooling, and is recommended for towing or high performance applications.

Oil Coolers are mostly used for air-cooled engines and race cars. Today’s many modern engines sometimes may not use an oil cooler for the engine. The engine's cooling system is usually adequate to keep oil temperatures within safe limits.