Pressure tested the cooling system today.

After applying pressure to the system I was able to see a super obvious leak in the upper radiator hose that somehow didn't show itself before.

I guess when the coolant is hot and flowing the leak would allow air to get in but not coolant to come out. Then when I pressurized the system, the coolant was static so it easily came out where air was getting in.

Ok.. tightened the hose clamp. It broke. Put a new one on and now system holds 15+ psi solid for 20min. In retrospect the dial on the gauge was sticky so it could have been leaking pressure slowly and not showing on the gauge...

Anyways, I'll throw the thermostat in next and see what happens!