Head Gasket

[maxwell6]

Wondering if I have a blown head gasket. This is the third time I pushed antifreeze out of the reservoir. It seems to be pushing past the 16lb cap. It only happens when i am wot or pretty close to. Other than that it runs fine. It is not over filled i left it down a bit after the last time it did it. And does not loose any antifreeze other wise. 4.6l 2v built with ported P I heads comp cams Trickflow Intake. Vortech Supercharged 14lb @550 rwhp. Anything else that might cause this issue. Thanks for any input.

[Laffs]

You're pressurizing the coolant system somehow. If it's only under boost and not mixing coolant/oil you might be lifting the heads under boost. Are you studded or running factory head bolts? I'd start with a leak down test see what results that yields.

[Ponyryd]

^Agree with above. Sounds like either heads or intake are lifting under boost. Could try turning the boost down a few psi.

[maxwell6]

Heads are studded

[bbriann]

Just a thought...
I ran into a situation a few years on my 2v that the heater core was collecting all the crap in the coolant system over the year to point where it blew off the hoses 3 times till i figure out what was going on...might be wourth trying back flush heater core or with hand on heater core inlet hose visually look at change in size a you rev engine ip...mine was quite noticeable...

[ZR]

^ could be exactly that, doing it before stat is fully open.

[maxwell6]

Thanks I will check into it. Planned on doing a flush and fill and rig something to power flush the heater core.

[bbriann]

Thanks I will check into it. Planned on doing a flush and fill and rig something to power flush the heater core.
Yep i rigged garden hose to heater core outlet and inlet to floor drain
and could not belive accumulation of stuff came out...after that the inlet hose stopped getting rock hard and expanding by 25%...

[maxwell6]

This might explain why my system it pressurized all the time. Should it be pressurized constantly even after sitting cold.

[ZR]

Well worth the effort to check. Be x tra careful getting those pesky plastic clips off the hose retainers (both sides must be released at same time, gently pull the hose off) without cracking the alum pipes.

[bbriann]

Another idea is could purchase a coolant pressure test kit off Amazon. I bought one because i thought smell coolant and was wondering about new heater core i installed. Turned out just residue left on top motor below intake, cleaned and smell gone. Anyway you could pressurize pressure test coolant system and see pressure/water drops just be careful not push water into cylinder if head gasket leaking...
My test pressure 13 psi dropped less 1/2 a psi in 6 hours ...that could be from coolant cooling down and hoses expansion.