Hi guys,

Got a problem with a BMW 318 (m43 e46), the cooling system used to pressurise so much that it created leaks, until one day it just blew a hose apart.
I replaced head gasket assuming it had gone and was pressurising the cooling system, and now after putting it all back together I discovered the outlet from the thermostat housing is not getting warm or pressurised, whereas the top hose is (mega hot, mega pressure), therefore I assumed thermostat stuck shut.

I just replaced that and it's still doing the same thing, thermostat outlet remains cold pretty much, and the top hose gets so pressurised I have to keep the cap off. After running it a while to see if the stat would open I finally gave up and switched off, at which point the coolant just started to belch out of the header tank so god knows whats going on inside!

All I can think now is the water pump? How can I test if it's working?
Engine running and cap off, there is no water flow that I can see. If I rev the engine it starts to circulate.

At a bit of a loss really, any advice or tips of what to check?

PS. temperature needle never goes beyond normal, nor did it before it blew hose apart - though it did after, so the sensor works!?