On mine, I noticed it was not getting to temperature on the dial. I checked on the climate, 19.2 or whatever, and it was never above low 70s.
I had it in for a thermostat replacement (at not inconsiderable cost!) and since then the dial sits bang on 90. But the climate always sits in the 83-85 region. This is not right, because when the car is stone cold it reads 5 degrees lower than ambient.
So I bought a new temperature sensor - the one for the ECU/dials is easy to get to - and it was then reading correctly with a cold engine. But after a long drive, it never got above ~75 degrees. Ebay rubbish...
Moral of the story is - don't bother wasting time and effort if the dial is in the middle