Head Gasket/Head????

Breadsnapper said:

Couple of months ago my 300Tdi started losing coolant (had to top it up once a month). The it overheated, as a result I have replaced all the hoses, thermostat, Radiator, expansion tank and cap and water-pump.
The issue I have is that when I start the engine the expansion tank has bubbles in it. I leave the car running to get it up to temp but all the hoses stay cold except for the by pass hoses and thermostat housing. The expansion tank continues to bubble, from the Y-shaped hose and all the hoses go solid as if filled with air. If I undo the brass radiator plug or the brass thermostat housing plug the pressure is released in the hoses and the expansion tank stops bubbling. Is this possibly the head gasket or even a warped head (car's not mine)?
I don't smell diesel in the expansion tank and the oil doesn't have water contamination.
Any ideas? I'm thinking it's the head gasket/head but after second opinions.
Cheers
Dave

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Datatek said:

If the hoses stay cold the water is not circulating, could be the stat, there are a lot of duff ones about, otherwise an airlock.

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Pikey said:

Head gasket gone can allow Exhaust gases to vent into a waterway. This will cause bubbles stick ya hand over expansion cap and watch for pressurisation of the system. or have a sniff test done at a local garage.

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