So I have been having issues with my 1997 A4 Quattro's engine overheating. On cooler days, or at night the air that blows in from driving the car is enough to keep it at a normal running temp. On hotter days the engine will start to overheat, but only just a little bit, usually 2 notches past the middle line. If you turn on the air conditioning it will jump up very quickly. I was looking around and found that the auxiliary fan was not spinning. I bought a new one figuring that was the problem, but when I plugged it in to see if it worked it didn't. I pulled out an external power supply and plugged it into the fan and got it working, then went and found the plug for the one in the car already and got that one to work as well.

So I'm thinking that the issue is a temperature sensor somewhere. I was looking through my Bentley manual and couldn't find anything about an engine coolant sensor, but I did see something online about how to replace it in an 04 model, but nothing on the 97. Anyone know what sensor it would be? Where I could find one? Or if there's some other problem causing this that I am missing? Thanks.

 

Could be your coolant temp sensor or thermostat stuck shut. The coolant temp sensor usually throws a CEL though. Any CEL/codes? When the car is at operating temp, open the hood and squeeze the top radiator hose. If it feels really hot and like its not filled up, could be your thermostat