Water/coolant temperature problem

A3Bash

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My 2008 S3 water temp seems to drop every now and then after it has hit 90 degrees. Even after a long 1 hour drive on the motorway the temperatue just slightly drops and then slowly goes back up. I've put it on a VCDS and there aren't any sensor faults. Any ideas? Thanks
 
Bash, it sounds like a sticking thermostat. This is a mechanical device, so would not show up on VCDS. I don't think that the thermostat element is too hard to get at, and probably does not cost much to replace. Good luck.
 
As above, thermostat for definate... Has the same on my old Golf MK4
 
Thanks for the replies, will have a look!
 
After an hours drive on the motorway it is quite reasonable for the thermo to shut and reopen. All it is doing is maintaining the temp at 90. Sounds to me like its doing its job.

If however the temp was not being adjusted back to 90 then i would see that there was a problem
 
After an hours drive on the motorway it is quite reasonable for the thermo to shut and reopen. All it is doing is maintaining the temp at 90. Sounds to me like its doing its job.

If however the temp was not being adjusted back to 90 then i would see that there was a problem

My temp guage never moves from 90 though, where as when the thermostat went on my Golf it would drop back etc.... Does yours move then Paddy??
 
The thermostat will regulate the temperature very accurately. No more than a whisker of movement on the needle. If you are seeing a difference in temperature, it's the thermostat which is not providing the usual fine control of temperature that we normally expect. Suggest you replace the thermostat and see the difference. Not expensive, but of course not a major problem also.
 
To be honest, well yes it does but only by the thickness of the needle. In traffic it will drop by more when the fan cuts in. the V6 has 2 rads and 3 fans so maybe its a bit more sensitive ? :)
 
This is my fourth audi in recent times and it's the first time I've seen it happen. When it moves more than the needle width it's a problem I think.