Coolant leaking out of cap at 20psi

[Jhnybravo]

Got a 2005 6.0 that's loosing coolant and I can't figure out why.
Back in Sept 2011 the oil cooler went out so my son and I tore the motor down, had the heads checked and magnafluxed (checkout out fine), replaced the oil cooler, did a package deal from Sinister with EGR delete, ARP head studs, black onyx gaskets, coolant filter, SCT Tuner etc. Already had a Edge CTS and currently the temperatures run around 200 degrees give or take 4 degrees. About three weeks ago, one of the glow plugs had gone bad and we replaced it and the wiring harness on the passengers side. When we got done we noticed that the coolant was low and have been chasing the coolant ever since. It comes out the cap apparently (which has also been replaced) and the pressure runs at about 18-20 psi. Any troubleshooting ideas? I've got no codes and the motor really isn't running that hot, just the coolant keeps disappearing!

Thanks much!

[the trav]

sounds like you are pushing water... suspect faulty head bolt torque OR bad head gaskets... black onyx ftl

[srjd]

I have heard it's best to stick with oem gaskets some people have had bad luck with the black onx I hope that it turns out to be something simple and I'm wrong

[Tuscany]

95% chance the black onyx gaskets failed. Your cooling system should operate at around 2-4psi no higher and if it's 18-20psi your gaskets are blown.

[devster55]

Bo did come out with a new design but I wouldn't trust em

[skanj0]

Sorry to say: Head Gaskets are gone

[asian195]

Not to hijack, but, if his black onyx gaskets did fail, does he have to send his heads to a machine shop again? Just curious for personal gain...

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[Tuscany]

Yes. Anytime you take the top end apart you should at least send them out to get checked for cracks and make sure the deck is flat. Not saying that they have to be machined but should always be sent out the be checked.