300 tdi problems

Hi having a problem with overheating bit of a strange one it will be fine for a while I could drive it for a few hours then all of a sudden it will blow the water out the cap or I could drive it for 10 minutes switch it off and when I start it there is no heaters I've replaced the thermostat and water pump. There is a valve between the thermostat housing and header tank would it be faulty as when you fill the water back up and take the plugs out the rad and housing the housing doesn't fill up with water?? Or head gasket? Any help would be appreciated
Thanks alister

And when I pour water in the thermostat housing plug it runs back to the expansion tank

could be head gasket ,the one way valve, is rad hot all over core once engine up to temp ,expansion bottle is connected to bottom hose so should fill rad easily but would be over flowing to fill thermostat housing , i usually fit cap on the bottle to fill thermostat housing ,an over full expansion bottle is no issue , heaters going cold is a sure sign of insufficient coolant

have you tried flushing the heater matrix through? maybe an air lock?


I could be miles off... but i know its a damn site quicker and easier than a HG replacement so worth a try!

Looks like head gasket just drove about 10 miles with no issue heaters workin fine and temp as it should be then all of a sudden heaters go cold and temp gauge shoots to the top and blows the water out??