You will find that most fan clutches are viscous or “fluid” (the internal friction of a fluid that is produced by movement of its molecules against each other. It is what causes the fluid to resist flowing) couplings that are combined with a bi-metallic (it’s a strip that is used to convert a temperature change into mechanical displacement and it usually consists of two layers of iron and copper) sensory system that is similar to that in a thermostat.
Sometimes fan clutches will fail on you but they are normally quite reliable so this doesn’t often happen. You will find though that a common symptom of the clutch fan failure is the car overheating when idling.
If you have a bad fan clutch, it can also cause very poor performance in the vehicle’s air conditioning system. The reason for this is because the fan also cools the air conditioner’s condenser and that is found directly in front of the radiator.
The other potential symptom if the fan clutch fails is that it will draw the air at a very high rate, so in the cold weather the heating system will blow out lukewarm air and it won’t ever deliver enough sufficient hot air.
It is best to leave the replacing of the fan clutch up to a professional mechanic, unless of course you know what you are doing. But if you are finding that the vehicle is fine on the highway, yet when you are in traffic or you are stuck at a red light and the heat gauge immediately goes up and gets too hot, then it may be time for you to get it replaced.
It is quite a simply process as the fan clutch is simply sandwiched between the can and the connecting shaft. All that would have to be done is to unbolt the fan and remove the clutch. The new one is then installed and the fan re-attached and you will then be on your way. It is advisable to may be do a coolant flush and put in a new thermostat at the same time.