This morning went from Sunny Coast down to Bribie Left at 8am Temp 14.5 C Noticed getting down the road car was running cold by about 15degrees. Was still under at 9 am when I got down there 90km later. Temp was up to about 16 by then. Coming home at 1pm it got up to 90 ok but temp was up to 24C by then. On the way down it was fluctuating between 75/85/90/ 75 . All over the place.

Rang the dealer suspecting something might have got disturbed when had belt and water pump done a few weeks ago and not used car much since. It has all the symptoms of a stuck open thermostat but they said it may be in the heater area. Has climate control and stays set on 22 all the time and was working ok today.

Anyone had similar problem and has a fix.
TIA