Weird temperature issue when warming up

[Mrmci]

Hi chaps,

Happy Christmas to you all.

I took the opportunity, arising from a break in the almost constant UK rain, to take the Elan out for a winter run and hit a snag.

After about 5 miles, with the heating on, the temperature gauge started bouncing and climbing ever higher. When it got above 100c I stopped and turned everything off. The heater was blowing warm (not boiling hot) the radiator was cold and the fan was off. I wondered if I'd lost all my coolant so opened the radiator cap and got sprayed in cold coolant......so clearly not.

When I turned the car back on, the temperature gauge settled nicely at 85c and stayed there with the radiator heating up normally.

Could it have been a stuck thermostat? Which was shocked open when I loosened the cap?

Any thoughts,

Cheers

Mark

[pharriso]

Could it have been a stuck thermostat? Which was shocked open when I loosened the cap?

Any thoughts,

Cheers

Mark

That would be my guess...

[EPA]

Probably a sticking thermostat but another possibility is some localised freezing of the coolant that quickly thawed when you stopped and the heat from the engine soaked through.
If obviously depends on how cold it was when you set off and the quantity of antifreeze in the coolant.
Ed

[Mrmci]

Good shout Ed but it's not been that cold in the UK recently.

[RichardS]

I had similar symptoms recently, and rectified by fitting a new thermostat.
Richard

[ill_will]

Hi Mark,

Was it working fine on the last run prior to this happening, and had you done anything to the cooling system since then (change the coolant, for e.g.)?

I've seen similar in other cars when there is air trapped in the cooling system. If it was working fine the sticking thermostat theory sounds plausible and is easy to swap out.

Cheers

Will