Rover 75 tempreture gauge

[Francisbernard]

I have a rover 75 1.8 saloon When I have the heater on (not AC) if i have the temp at about 22-23. Once I get over 85mph the gauge starts to fall away and the interior starts to cool down. if I slow down or switch the heater off the gauge returns to the halfway position and off we go again. I have taken the car to two garages neither of them could find any fault. A pressure test was done no prob's with the head gasget, all hoses are getting hot no air locks.. Can anyone help Frank

 

[^neo^]

its a rover.
With the current weather the air temperature probably cools everything down more than the dinky little engine can produce heat.
You can try blocking off a bit of the radiator with some cardboard so less air flows through it

 

[75pete]

Post this question in the Rover Forum. Lots of people up to speed on the 75