Overheating VY Supercharged Calais

[sam]

hey guys just bought a vy supercharged calais,it overheated on a drive up to tweed heads from byron bay,blew out the side of the radiator,was jetting out air from the bleed screws so i assumed the worst and removed the heads,got them skimmed and crack tested then cleaned the block put new head gaskets on and refitted them with new headbolts to the block etc etc. filled up cooling system and bled air out of all 3 bleed screws.

replaced thermostat and radiator + cap, car started and ran perfectly. drove it to work and back,checked the car when i stopped.no leaks, checked in the morning before i used the car and found the top radiator hose had split, so after ive turned the car off the cooling system pressure has continued to build and caused the weakest point in the system to split,in this case the top radiator hose.

now ive replaced the hose,refilled the cooling system,re-bled the air out of the system and the cars started overheating again. thermostat is opening,no external coolant leaks,no water in the oil. there was a bit of oil residue under the radiator cap though.

now im wondering what possibilities are left. is it possible a couple of fins have broken off the water pump and its not cerculating enough coolant through the system and its overheating, blown head again???

the thermo fans are cutting in,i can feel air bubbles in the top radiator hose, also when i turn the car off the temperature goes up higher on the guage,had to leave thermo fans on.

im a bit stumped by it.
tested the bubbles coming out of the radiator with a c02 tested, fluid remains blue (good), and pressure tested and holds pressure.
has anyone had any problems with the water pumps before?
any suggestions would be greatly appreciated.
from sam

[TMM]

The water pumps are not expensive for these engines, i'd just replace it anyway. Also do the heater tap while you're there - another cheap plastic part that likes to crack and leak.

The 3.8L V6 (Ecotec/Supercharged) are an all iron design so you generally would not expect the headgaskets to fail from a minor overheating.

[scvs6]

A VY Commodore with a Supercharged V6 came into work last year because it had an overheating problem, after checking everything, we noticed the water wasn't circulating. So we pulled the water pump off and all the fins were gone. It never had coolant in it (just water), so they just rusted up and broke off. So we fitted a new water pump, coolant, bled the system, and it was fine after that.