Re: 1999 Jeep Grand Cherokee Radiator Fan
Good Evening rocke70, I am not familiar with that particular vehicle, but generally the system works like this....
There is generally a thermal sensor switch located on the radiator, most often near the bottom, (but it may be in one of the water galleries on your machine) this usually operates in the region of 85 degs C, this then normally would operate the fan relay which in turn operates the electric fan.
The electric fan should really run with pretty decent guts and will be hard on fingers if you are in the way, it usually only needs short runs to drop the temperature.
There is generally a second electric fan associated with the airconditioning system, don't confuse which fan is which, the A/C fan should run most times when the A/C is functioning and is not as powerful as the engine cooling fan.
Most often the thermal switch is the problem when vehicles overheat, (provided that the system and thermostat is otherwise operating properly) I would suggest examining the thermal switch system urgently, it is also possible your fan may have a problem in it's motor and is not operating properly .
I can't explain why you are seeing a mediocre operation with it.
I generally identify which switch / sensor is involved and remove and place it in a saucepan of hot water with a meter lead attached and carefully ensure it is operating before the water boils.
Generally the fan switch / sensor only grounds a current path to operate the fan relay.
I hate seeing aluminium clinder-headed vehicles overheat, generally it starts a chain of nasty events.