An oil cooler reduces the temperature of lubricating oil. Oil which gets too hot can break down and lose its lubricating properties, and an oil cooler can prevent this.
Oil coolers are most commonly used to cool engine oil, but similar systems can be used to cool transmission or axle oils, or power steering fluid.
At its simplest, an oil cooler can be nothing more than a length of tubing which is placed so that it is cooled by passing air. For greater cooling effect the system can incorporate an oil-air heat exchanger which looks similar to a car radiator and works the same way.
