An oil cooler is designed to remove excessive heat from the oil used to lubricate vehicles, machinery and mechanical equipment. For example, a hot engine transfers heat to the oil which then circulates through a heat-exchanger (also known as an oil cooler), using either air or water to cool the oil.
Oil-cooled engines use engine oil circulated through an oil cooler. Liquid-cooled engines use a mix of water and coolant circulated through a radiator.