Dalek cap

[necromonger]

Can anyone tell me how you tell if the dalek cap if faulty, and can a faulty dalek cap cause the engine to stall when the water is hot, through not releasing the pressure?

[kevtherev]

the cap allows coolant to pass to the top up tank after 1 bar pressure is reached. (expansion of coolant)
it will have no resistance returning to the header.

no it won't stall an engine.
unless the engine got so hot it seized

[necromonger]

Ok thanks for that.
DG 1,9 petrol 1987, the reason i ask is that the van starts no problem drives ok, but when up to temperature the revs die and the engine stops. Start the engine but no power to pull away without over reving.
When setting off the water in the expansion chamber is about 1/2 to 3/4 full but when the engine stalls the expansion chamber is full to the top.
I have removed and checked the water pump all ok, i have replaced the thermostate checking it in hot water to make sure it opens, which it does, parked on the biggest hill around and bleed the system, rad gets hot top to bottom left and right, changed the temperature switch below the thermostate, but the water light sometimes stays on, when its really hot i get the buzzer of doom, stop let it cool down, remove water from the expansion chamber and it starts and runs ok, it gets hot and the expansion chamber is full again, could it be drawing water from the radiator but not letting it flow back, thats why i changed the thermostate, even though when testing the original that seemed fine and opened when testing it bowl of hot water.
So the only thing i could think of was the dalek cap may be faulty.
Any advise on what else to try ?

[kevtherev]

The idle problems when hot may not be connected if it runs ok when cool.
That would suggest an air leak,
search "air leak" and "stalling at junctions", you will understand why.

the issue you have with coolant needs properly investigating
firstly lets get the terminology right so we are in understanding
the tank behind the flap is the top up tank or expansion tank, the tank inside the engine bay is the header tank.

as you describe the top up tank (expansion) fills when hot and does this overflow?
is there air or a constant stream of bubbles in the header tank?
did you bleed the system following the baxter method on Brickyard?

The flashing red light indicates too high temperature and/or low water level in the header tank
the buzzer indicates the oil is so hot that it can no longer maintain pressure at low rpm because it's thinned out

some things you may want to consider
a combustion gas sniff test of the coolant to eliminate a head seal rupture
a blockage in the cooling system/radiator