should the temperature gauge stay at 90oc when up to temperature as my gauge never used to read anything so put it down to a dodgy thermastat, just had a cambelt service and had a new water pump and thermastat fitted at the same time. when the car got up to temperature the gauge went up to 90oc and would stay there problem solved happy days , that was 2weeks ago. this morning however on the way to work cruiseing down the motorway car up to temperature gauge reading 90oc slowed down to exit the motorway and the temperature just dropped once back up to speed it went back up to 90oc again.when i got to work popped the bonnet had a look no leaks or loss of water no loose connecters that i could see. on the way home from work it did the same. does this mean the thermastat has failed or the sender is know playing up or is this normal.the last 2weeks i've done loads of miles and it never once dropped like this once up to temperature.any ideas?????????