The fan sensor, also called thermal switch, is responsible for turning on the engine fan in the right moment, i.e. when the coolant temperature exceeds a predetermined value. When worn, the sensor requires replacing. In the event of a failure, the fan may operate continually, irrespective of the engine temperature, or stop operating at all, even after the critical temperature is exceeded, resulting in engine overheating.
What is the role of the radiator?
The radiator is one of the most important elements of the engine cooling system. Hot coolant flows through it to be cooled by the air flowing around it while the car is moving. This way, excess heat is removed from the engine. When the car is stationary, the necessary air flow is provided by the electric fan.
What is the role of the thermal sensor?
To prevent the fan from working continually and from cooling the engine when not required to do so, e.g. in winter, the cooling system is equipped with a fan thermal sensor. After the coolant reaches the critical temperature, the sensor causes the electrical circuit to close and, consequently, the fan engine switches off.
How is the fan thermal sensor changed?
Like any other electrical device, the thermal sensor may brake down. If this is the case, the fan may work continually, irrespective of the coolant's temperature, or worse, it may not switch on at all, even if the engine temperature goes beyond the limit. In such case, the thermal sensor must be replaced by means of removing it from the element of the cooling system in which it is fitted, usually the engine head or a radiator hose.
What to keep in mind
As removing the switch requires opening the cooling system, it should be cleared off the coolant beforehand. Next, after disconnecting the electrical plug, the faulty sensor is replaced with a new one. After reconnecting the electrical system, the coolant is refilled to the required level and the engine is turned on to check if the radiator fan operates properly. It is also possible to check if the vent switch works properly by means of connecting it to a diagnostic tester.