Blown head gasket most likely, or cracked head. been getting intermittent white goop under the cap off and on for a few months now. initially thought it was due to the overnight temp swings of the seasons changing -- common symptom of Head Gasket Failure Denial.

so what happens here? cylinder gasses pressurizing the cooling system, and boom? I don't know much about the cooling jackets and where they run through the head and block, but I'm assuming there's a gasket leak near one of the cylinders.

also seem to be getting some blow-by as well. I'm noticing a film of oil collecting around the breather I have on the front of my valve cover.

I can only imagine the expression on my face when this thing let loose

The coolant passages are only about 1/4" away from the cylinder. It's surprising that more head gasket failures don't have catastrophic results like yours. After all, 150 psi compression pressure getting into a cooling system designed to run at 15 psi could blow up a radiator or heater core, as well as a hose.

isn't that what the radiator cap's for?
I never heard any boil over.
Wonder how frequently caps go bad.

got some info from EB. will check out a few things and post back if I find anything interesting.