Originally Posted by tabetha

4wd and 2wd stats are different, 4wd one a lot more, not sure on cap price but is VW.
I would firstly make sure the de-gas pipe to the expansion tank is clear, and don't top up over min level, keeping it on min is fine.
The systems on these degas perfectly, if ok, so any air left after the first heat up and cool down is not trapped air but is created most likely by a HG.
It is normal for the coolant to bubble, as it gets hotter when you switch off, and helps to draw out any air(de-gas).
If you watch it after doing a a/freeze change you'll find that about 10-15 mins after switching off it will bubble lots, then stop as the air comes out into the tank and the level drops a bit.
A dicky cap can cause water loss as it lowers the boiling point over a working one.
tabetha