2003 Audi A4 Avant 1.8T Manual...

Symptom 1 - The engine temperature is slow to warm up.
The temp goes down when I go downhill and there is no load on the engine. This points to a thermostat that is stuck open.

Symptom 2 - The electric radiator fan turns on when the car is cold, preventing the coolant and engine from warming up. The fan stays on for quite some time. When I turn the car off, the fan also turns off (i.e. - it doesn't keep running when the engine is off)

Symptom 3 - The heat in the car is slow to warm up.

EVENTUALLY (40 min of driving), the car will reach normal operating temperature and the radiator fans will turn off. The car's cooling system functions normally after this. However, when the car sits and cools down after some time, the same symptoms return when I start-up again.



I have already searched some of the threads and found SOME answers, but none that are definitive. So, hopefully some of you professionals have some answers for me...



Questions..

What controls the radiator fan? (ECT sensor on the back of the engine block, another coolant sensor that controls just the fan, thermostat itself)

What controls the opening and closing of the t-stat? (T-stat itself, ECT sensor, other sensor in the radiator or hoses)



Here is why I ask those questions...

If the T-stat controls the fan and it is stuck open, it seems like I need to replace the t-stat. However, if the ECT sensor on the back of the engine block controls the t-stat (open vs close) and the fan, perhaps I need to replace that sensor again. Or, perhaps there are other sensors in the cooling system loop that tell the T-stat to open/close and the radiator fan to turn on/off.



Lastly, I could be missing something all together with my elementary understanding of engine temperature management, so please let me know if I'm way off the mark.


Thanks in advance Ls and Gs!!

 

Is the check engine light on?
Is there a map cooling faults?

The ecm will keep the aux cooling fans on if it sees any cooling system faults stored.