Strange cooling problem

[coolngroovy]

After about 10mins of driving, the temp gauge hits 3/4, the dash warning light & siren go off, then the temp returns to normal & all is good!
VS Caprice, eco.
Anyone have an idea?
Cheers, Col.

[vsiicalais]

could be a faulty thermostat or a possible partial blockage of one of the pipes but im guessing its more a faulty thermostat

[hako]

I'm with littlegeorgy01 - thermostat sticking when cold then once forced open behaves normally.

[coolngroovy]

I will change it. Thanks.

[Harvs82]

Failing that, your temperature SENDER (the one that controls what is shown on the dash) could be faulty too. When the gauge is showing 3/4 is the cooling fan coming on? If so, does the temperature drop down again?

[coolngroovy]

yes it does.

[coolngroovy]

Update.
Loosing coolant. No visable leaks.
I took the rad cap off & started the engine, when the thermostat opens there is a steady stream of bubbles!
The heads are coming off next weekend!
Car has 105000ks, it sat in storage for 3yrs before i bought it.
Looks like it didn't like the rest!