You think its stuck open then?
Cheers
adam
Yes. I am going to crawl under mine tomorrow to (hopefully) fix exactly the same fault.
While you are driving with a stuck open thermostat you will be using too much petrol. The car takes a long time to get up to temp - especially noticeable on short journeys.
And when you are driving at 75° the oil will be thicker than it should be (at 90°) so will create drag and further reduce your mpg.
My AGG did a trip from Warrington to Hedge End (about 220 miles) with an average of 46.6 mpg and 60 mph the other day - a record for me and I was well chuffed. It was a warm day so the temp was at 90 most of the time which must have helped.