A car's radiator is used to help keep the engine cool. During operation, an engine's moving parts create friction, which produces heat. Even with the use of engine oil for lubricant, the heat from an engine's natural friction can be enough to damage the engine if it is not kept cool by the radiator. Once the engine reaches a certain temperature, the radiator is engaged to keep the engine from overheating, which, if it does, can cause catastrophic damage.