Help needed mk3 golf 2.0 gti 8v AGG cooling problems

[golf-gti-matt]

Well i recently got this golf off a guy that was going to scrap it he said i could have it for nothing so i took him up on his offer, it was overheating and pressurising the coolant.  I drove it home (about 5 miles) it didnt overheat just sat at 90 degrees on the coolant temp gauge, when i got home opened the coolant tank it was under alot of pressure, i thought head gasket.  So i have replaced the head gasket, just finished and fired her up.  Perfect at 1st, coolant was steadily sat in the header tank, then as it got to about 90 degrees the level dropped and the bottom hose became warm.  Superb.  But then as it got hot the coolant started to really spit out of the header tank and make some horrible noises and the level kept really going down, i thought it was just air in the system so ran it for about 10 minutes.  The coolant temperate gauge stayed at about 100 degrees so the fan wasnt cutting in.  I looked at the oil temperature and it was 112 degrees so i switched it off.  There was no real smoke coming out the exhaust it was all clean there.  Whilst i did the gasket i changed the thermostat and made sure the rad wasnt blocked.

Any ideas what it could be? 

cheers

[boneybradley]

compression test time...could be a cracked/warped head!

[golf-gti-matt]

Would be a real shame if it was.  Its ok when its cold but as it gets warm the coolant in the expansion tanks begins to boil and all the pipes at the top of the engine get very hot, but the radiator and bottom hose are both fairly cold, luke warm at most.  There is no smoke and no oil in the coolant.  Also if the water was being compressed would coolant shoot out the tank everytime you blipped the throttle?