Why does your radiator fan keep going on and off?

An automobile's radiator fan will switch on and off during normal operation of the vehicle, and sometimes after the vehicle is shut off. The fan is controlled by a thermostat that regulates the temperature of the coolant in the radiator. When the coolant rises above a certain temperature, the thermostat switches the fan on to cool the radiator until the temperature drops below its limit and shuts off. The fan turning off and on is a normal part of the car's operation and is nothing to be concerned about.