454 mercruiser puking water

[n514bm]

Hi all. I have a 454 rebuilt professionally 90 run hours ago (3 years) that is freshwater cooled. At 2800 RPM, temps stay cool, but I am puking foamy water from the cap.
Does anyone know of a common location in the manifolds or elsewhere that might explain this??? Or possibly a stuck thermostat causing the water pump to cavitate??
I might have to rig up a leak down tester off a scuba bottle to check the cylinders.
Thanks for any help or thoughts.
Brian

[FlatRat]

:) I don't think a stuck stat will do this.Sounds like a head gasket.Has it ever got hot?A leak down will tell the tale.Good luck

[H2OT TIMES]

I have to cosign the head gasket theory.

[SmokinLowriderSS]

I have to cosign the head gasket theory.
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