A car engine burns fuel and uses friction to give your car motion. These processes cause a great amount of heat to build up in the engine. If this heat is not diverted away from the engine, it can cause the pistons in the engine to seize up in their cylinders and eventually snap; causing engine break down.
Some of the heat escapes through the exhaust system. Oil is used to lubricate the internal engine parts and cut down on the friction. But oil and the exhaust system by themselves are not enough to get rid of the excess heat. A car engine runs best at an average of 180 degrees F. Once the temperature reaches 200 degrees F, the cooling system has to kick in and help to cool the engine.