820 Vitesse coolant problem

|| Hi, || || Recently, we've had a few very hot days and on completing a 1/2 hour || journey, the radiator header tank has been so full the coolant is || escaping from the cap. Anyone any idea why this should be? My only || guess is maybe the thermostat stuck shut? || || Regards, || Aaron.

Apart from worst case scenario that the cylinder head gasket is on its way out..

first thing to check.. is the radiator cooling fan coming on? if when you stop, its that hot the fan should be on... if not most probably thermostatic fan switch.

if the radiator is stone cold and the water is coming out of the header tank, then it is either the thermostat or an airlock (unlikely to suddenly occur though)

Des

I've had this before on a Citroen BX (no expansion tank, though - cap is on the radiator). It turned out to simply be a duff cap - the spring had weakened, allowing the pressure to drop and hence the water boiled at a lower temp, which caused more steam to escape, which caused the pressure to drop further....... and so on.

Probably your cheapest / easiest fix to try first.

Ade

Thanks for the suggestions, will check them out. Mechanic was doing a suspension bush on the car today cos i didn't have time and when asked, he suggested head gasket too, but there's none of the signs i expected - unseen loss of coolant, "mayonnaise" in oil filler cap, moisture on dipstick.

Aaron.