Looking for solution to this problem.
When driving normally (no boost) everything works fine, engine temperature stands still.
When going boost, coolant pressure rises and temperature rises instantly. After that its hard to cool engine with light driving or even at idle.
All coolant hoses seem to be conected properly, no coolant leaks.
Any ideas what can be the problem?
Car is EG5 with swapped B16A2, boosted.

 

99.9% headgasket.

 

yep Blown head gasket or the head bolts are stretching under boost.

 

ok..
can I use ARP head bolts from B18C? will they fit B16A?
Luckilly I have some headgasket lying around...

 

Also make sure you properly fill your radiator system. You don't want to get any air bubbles in your coolant system.

 

radiator filled properly, no air bubbles in coolant. double checked that.
might it be some airleak thru throttlebody?

 

I had the exact same problem. Did every single step of troubleshooting still boiled under boost. The culprit was the headgasket.

 

headgasket, I had the same problem