Erratic coolant temperature gauge?

[Nessy]

Just a quickie.
The last few days my coolant temperature gauge has decided to play up for a few minutes on my drive to work.
Cruising at 70mph, the gauge will gradually sink from 90 to about 65 for a few mins and then just go back up to 90 again, it did this once on the way home from work today (40 mile motorway drive).
Don't think its the thermostat as its only about a year old (though I accept that's no guarantee it's still OK), am getting roasting hot air out of the dash vents and the coolant temp (from CTS?) via the climate control panel reads 90 degrees (block 51 right?) all the time the gauge is playing up.......
Any ideas what might be causing this?
Problem with the dash/gauge or could it be the thermostat?
I'd rather it be the thermostat than an issue with the gauge or dash tbh........all other gauges eg oil temp, voltmeter,fuel etc work perfectly .

Thanks!

 

[Bradderz_1988]

Mine used to do this on my way to work on the motorway (maybe a month after i replaced the stat and CTS which were both genuine) and its never done it since, all the gauges on the car work fine the fuel gauge seems to be a little optimistic at times i can start it from cold with just under half a tank and after a few miles of 'grandad' driving it will go up to more or less half way between 1/2 and 3/4

iirc the fuel gauge being abit temperamental is a sign of the clocks about to go is the true or just utter bull**** ?? Lol

 

[aragorn]

Its block 49, not 51. 51 always shows 90 once the engines warmed up. 49 shows the actual temperature.

My votes on the thermostat.

 

[Rogerx]

It is not the thermostat, it is the ETC just had mine fixed.

 

[Nessy]

Its block 49, not 51. 51 always shows 90 once the engines warmed up. 49 shows the actual temperature.

My votes on the thermostat.

Thanks as usual, I did wonder why the reading on the climate control panel just sat at 90 and didn't move after it had reached that figure.....it didn't play up at all on Thursday though.

It is not the thermostat, it is the ETC just had mine fixed.

What's ETC please?

Never heard of that before?......

 

[aragorn]

Never heard of it either.

Maybe he means the coolant sensor, but in my experience the thermostat fails far more often than the coolant sensor, and it being a year old doesnt preclude it failing either! I've had some fail out the box, and others last less than a year.