Random temperature gauge on Altea XL 2.0 TDI 170

[Stewart Russell]

I have a very strange thing happening to my Altea. If I drive until it is warmed up to 90C and then have to stop for any reason the temp gauge goes to 130C and the fans kick in and it says check coolant. Once revving the engine or driving off it goes back to 90C. Even on the motorway if I decelerate the gauge tries to climb and then when I accelerate again the gauge goes back to 90C. I have changed the coolant temperature sensor but this has not solved the issue. Does anyone have an idea what is wrong. This is driving me mad but I don't want the expense of taking it to a garage.

 

[martin j.]

Thermostat not opening fully? When stationary there’s not enough coolant flowing to the rad and when moving the airflow helps cooling, or water pump failing? Does the temp stay normal if stationary but with the engine at a fast idle?