It could well be the culprit and no it does not show up on VCDS or at least not on PF. My S8 was heating up to 120C and slowly loosing coolant through the cap couple of years ago in slow traffic. It turned out that electrical fan had failed and valve was stuck in coolant reservoir cap letting the pressure and coolant to escape when getting too hot. Second hand fan and new Febi cap later normal service was resumed.

Thanks Ainars. Is it the fan motor that fails? And should i be able to see it running at normal operating temperatures?

Usually the motor seizes up and pops the fuse. It should come on with the AC.

Thanks MJ. Does it have it’s own fuse? And, if the air con (AC?) is on, should the fan be running?

Yes, there are three fuses - one for each speed - all in the passenger side electrics box. It should always be on the 1st speed when the AC compressor is running, ie not in 'econ' mode.

Mine was not seized, just not running. IRRC it should run at slow speed if AC is on. I got replacement fairly cheaply so never investigated if it had bushes or sliprings worn out.

Both fans are working and it’s still overheating :(

Might be your viscous fan clutch, Jim. When was it last changed?

I believe you can check it by seeing how easily you can turn it by hand when the engine is hot (*without the engine running!).





*Unless you're feeling brave and/or stupid ...

https://www.youtube.com/watch?v=wEnY9oXW9PU

https://www.youtube.com/watch?v=cOXcrbQRDWU

It’s never been changed since I’ve owned the car. I assume that I shouldn’t be able to turn it easily by hand?

If I understand correctly how it works, you should be able to turn it fairly easy by hand when the clutch is cold but the turning resistance should increase as it heats up.

They do tend to fail/wear out I believe. I usually have mine replaced at every major service. I should have the last one that was replaced here somewhere, which was working when it was removed. You're welcome to have it if it turns out to be that, although it might make more economical sense to fit a new one.