Hi guys, please help, I've got an A3 2l tdi sportback s-line, 2008.

Audi A3 S-Line 8p tdi

Registered User
So the problem i have is the small cooling fan running all the time from when I start the car to when I turn it off. It starts and stops constantly, also I have lost my temperature gauge, the needle never moves even when the car eventually warms up with the fans constantly going. I've replaced both sensors but not sure if they could still be the problem? I assumed they are the same so I have a matching pair, they are the grey ones. One on the thermostat housing and the other near the air intake pipe. I was wondering if the fans and the gauge are linked and if that can better help me diagnose the problem.
 

samisnake

Registered User
If your car can't get a temp reading or recognises there is a fault, it'll run the fans. It's safer to have the engine running cold than overheating. I would say that the fact your temp gauge shows nothing is linked to your fan running.

Get the car plugged into a tool that can delve deeper than basic obd2; vcds, obdeleven, autel maxisys etc. Hopefully that narrows the issue down further.

I have seen it on my mates audi where a failing thermostat caused s the fan to run constantly, never seen the temp gauge die though.
 
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Audi A3 S-Line 8p tdi

Registered User
If your car can't get a temp reading or recognises there is a fault, it'll run the fans. It's safer to have the engine running cold than overheating. I would say that the fact your temp gauge shows nothing is linked to your fan running.

Get the car plugged into a tool that can delve deeper than basic obd2; vcds, obdeleven, autel maxisys etc. Hopefully that narrows the issue down further.

I have seen it on my mates audi where a failing thermostat caused s the fan to run constantly, never seen the temp gauge die though.
Hi thanks for the reply. I understand that the fans with run as a failsafe to keep the car from overheating. I'm just very confused, I've removed the thermostat and tested it in hot water, it was closed when I removed it and opened up when in boiling water. So I thought it can't be the thermostat but a new discovery is that my water is circulating instantly in the expansion tank from startup, surely that points towards a stuck open thermostat? I just expected it to be stuck open on removing it if that was the case. I'm going to get the car plugged in I just wanted to eliminate anything that could make diagnosing the problem easier. I think I'm going to get a new thermostat and two more coolant sensors from Audi as I need to eliminate these as a possible cause. I don't trust those cheaper sensors. I will let you know how I get on.
 

Audi A3 S-Line 8p tdi

Registered User
Mine was a combination of the fans and temp sensor near air inlet.
I've just purchased and fitted a second hand complete fan unit as one of my fans didn't work. Now they both run but constantly, so both fans work and both coolant temp sensors are new genuine, I'm not sure what else to check. Does anybody know if there is another temp sensor for the fan, like a fan temp switch? Winter is coming and my car is not going to like it with both fans constantly running. I'm worried it's going to ruin my engine. Thanks for any advice
 
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