Hi - long time no see everyone!

I come back when i have a problem - sorry!

My friend has replaced the thermostat on my A3. Following this, the temperature gauge is still not really working, it normally hovers at around 75 still (same as before he replaced it) and it made it up to 90 once when i was doing a little motorway driving.

Since he's done this it is drinking my diesel at an alarming rate, much more than usual.

Any ideas what's wrong?

Am just fed up with it now, it's cost me a lot of money the last few months in repairs so i just want rid really but at the same time i don't because i've spent so much repairing it and might end up buying another that also needs work doing