I've got a 1.8T Sport '98 A4 and the water temp is all over the place!
The interior of the car can be warm yet the gauge is showing 60 - 70, sometimes it does rise to 90 but then settles down low again.
I have changed the temperature sender and the fault is still there, it used to work perfectly until about 1 week ago.
Any ideas?? My first thoughts are the gauge itself. Thanks in advance.