It was the throttle body gasket. After I installed it I pressure tested the coolant system. I also had a leak at the temp sensor but after tightening that I had no pressure loss at 10psi over 3 hours.
It started up fine, took about 20 minutes of idling to blow most of the coolant out or burn it off. Idled nice and healthy, though it was noisy due to the HLA's needing to fully prime.
I am about half way through the retorque and I have an oil pump leak to deal with. I used a plug where the old sensor was as I added an aftermarket one. But other than that she's ready for the road.
Also, I noticed there's no pressure values for the cooling system in the FSM only head pressure. For that 20 minutes mine sat right around 4.2psi. Not sure if this changes with extended driving but I'll post if I notice a pattern.
What a learning experience. It was quite disheartening at times.
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