I have been having an issue for about a month now where my coolant system over pressurizes and fills my overflow. it will be fine for about 40 miles then it will start to over heat because of the lost coolant. i removed the thermostat just to see if it went out on me but it still does the same thing.

When i am bleeding the system, i put a filler in place of my rad cap and keep that filled, since i do not have a bleeder screw on the top hose housing. so when i am bleeding, during idle, bubbles rise to the top like normal, coolant goes down and i keep it filled so it does not suck in air.

When it stop lowering, it will still bubble, but not take any, once i rev it up, it stop bubbling, once i go back to idle, it will bubble a lot then have tiny little bubbles. I just changed the head gasket thinking it was the reason. Still doing the same thing. I have arp head studs trq to 87. i replaced the bypass hose, top rad hose, and heater hose. system is fully bled and if i drive it, it will still over pressurize.

what else could be the issue? i would have changed the rad cap too but the bubbling has got me lost.... theyre small bubbles.

 

I would test the cap or replace

 

you swapped the headgasket but were the surfaces flat?

 

Welp, doesn't matter anymore. Think I just cracked a sleeve, which might have been the issue to begin with. I have an *** load of coolant in my oil.