Apple, if your car is overheating it means there's a problem with the radiator (leak, blockage, damage). There's no danger of the car catching fire or exploding.
Cars catching fire are usually the result of electrical faults. Sometimes it could be a fuel pump or combustible material reacting with the heat.
The temperature gauge in cars is a measure of how efficiently the radiator is cooling the engine. Some sports cars come with an engine oil heat gauge.
Never let the temperature gauge reach the max or you might be looking at an expensive engine repair job. Switch the engine off immediately. Also, you need anti-freeze in the radiator, not just water.

 8,000 Graphics and Pics