MelloYellow

We're getting pressurized coolant with our new forged longblock and Vortech S-Trim.

Can anyone help point us in the right direction for troubleshooting this?
My mechanic is thinking it's the heads.

Any help appreciated.

1fastWS6

iTrader: (3)

Head gasket most likely....

crainholio

iTrader: (2)

Two options for diagnosing a cooling system problem like this:

1.) NAPA sells a $50 kit to check for hydrocarbon presence in the cooling system. Remove the rad, fill the test tube thingy w/ the blue liquid it comes with, hold it to the rad cap w/ the engine running...if it turns yellow, you got HC contamination.

2.) AutoZone rents/loans a tester that you attach to the rad in place of the cap. Pump it up to 16psi or whatever your system is rated at, watch for the pressure to fall rapidly. If it does, you got issues.

I'd start with #2 as it's free and fast, if it fails that test you can either move on to test 1 to see if it's combustion pressure.

MelloYellow

Will add more in a bit, but does look like a headgasket.
I think we're getting a poor seal with the Cometic.

We're going to switch to a GM MLS.
Can anyone confirm the gasket bore of a GM MLS?

Also, our tolerances were too tight. Our head chamber ended up 3.907" and the gasket 3.910".