Your vehicle's road performance greatly depends on the cooling system. And when we say cooling system, we don't mean just the radiator. There are other important parts that the cooling system cannot run without. One of them is the fan clutch. The OEM BMW fan clutch's function is regulated by a valve that is opened and closed by a thermostatic spring. This valve is responsible for controlling the flow of a viscous fluid between chambers in the BMW clutch assembly, allowing the fan to function according to the engine's temperature. The clutch partially disengages the cooling fan when the engine is cold, making the fan turn at a low speed.