A motor vehicle engine generates a considerable amount of heat whilst it is running. The engine needs to be kept cool to avoid the damage that can be caused by overheating. To combat this problem all vehicles are fitted with a coolant system. An integral part of a coolant system is the rad (radiator) fan switch.

The rad fan switch works by way of an electrical relay. This relay has sensors to detect the temperature of the coolant in the radiator which is circulating around the engine to keep it cool. When the sensor detects that the temperature of the coolant has risen to a certain level it switches the rad fan on. This has the effect of blowing outside air across the radiator. This, in turn, results in a reduction in the temperature of the coolant.

A faulty rad fan switch will result in the coolant temperature remaining high, which will cause the engine to overheat. The first sign that there may be a problem with the rad fan switch or one of its components is a warning light that the engine temperature is too high. To avoid the damage that this can result in it is essential to replace the faulty part as soon as possible.