Radiators are part of an internal combustion engine's cooling system. Coolant or water is pumped through the engine. As the coolant cools the engine, the liquid itself becomes heated, and is pumped into the radiator, which radiates the excess heat to the atmosphere, allowing coolant to re-enter the engine at a safe temperature.
Causes
Overheating can be caused by defective thermostats, inoperative cooling fans, defective radiator caps, loose water pump fittings, coolant leaks, or damaged radiator hoses. Anything that causes the coolant to stop flowing through the engine will cause the engine to overheat.
Consequences
The first sign of overheating is the engine making a pinging noise and starting to lose power. Hot spots can develop, which can damage the engine's pistons. As heat increases, aluminum parts of the engine will swell up, which can cause the head gasket to burst. If the coolant boils, the radiator or its hoses may burst, which can result in extreme damage to valves and pistons.
What to Do
If your radiator overheats, your heat warning indicator should come on. Stop driving immediately, and let the engine cool down. Add coolant if possible before trying to drive, even just to get the car to a mechanic. Check for loose belts, fan failure, a dirty radiator or cooling system leaks.
