Why the fan on my 2000 jetta mk4 always on?

Question

the fan on my jetta is always on even in cold weather. sometimes even when the key is not in the ignition. what can i do fix it

Answer 1

replace the sensor that controls the fan, when these fail they usually default the the closed state so the fan always runs

Answer 2

When you drive your car and the engine get too hot for the speed you drive(not enough natural air flow thru the rad to cool the coolant) so the rad fan kicks in to cool the coolant so cooler coolant enters the engine to cool the motor.
Just because you shut off the engine does not mean the engine is cool yet so the rad fan keeps on going for a little while longer. No big deal. It is just finishing its job. It is totally independent of the ignition key, for after you stop the engine is when the coolant stops circulating and the heat really builds in the engine. So the additional fanning helps to cool the motor down too.
If however you find that you battery is dead the next time you try to start the car....the temperature sensor has become faulty and allowed the fan to keep running after the prescribed has been reached.
It must be replaced.
These sensors will either stick "on" or stick "off". When they stick on-you can tell cause it will run when the temp gage is reading cool. You could buy another sensor or wire a toggle switch in line so that you can "turn it on" when the engine is too hot. Which means you would have to keep an eye on the temp gage every once in a while. It would get hot in stop and go traffic, when you are following behind big trucks and long hills upward.
But the fan is normally on only because of the lack of airflow thru the rad or that you have a blockage in front of the rad(cardboard or a bra)

Answer 3

it should stay on when car is off to cool it down or your low on coolant or some one jumpped the switch as i described earlier and left it that way its okay to drive like this but not hot hot is very bad cool is okay