there is no coolant flow through anything when the thermostat is closed.

when the thermostat is closed the temp you see is block temp, anything over boiling causes cracked heads/blocks and warped engine parts.

Not even the heater core?

Keven, I was simply using my experience as an example. I did correct my mix though.

If you're still leaking water, check the area around your heater hoses. The upper hose feeds to the heater and there is a flow restrictor in its elbow, the lower is the return. There are arrows on the tensioner that indicate flow direction. If someone replaced the main tensioner lately they could have screwed one or more of the five o-rings associated with the tensioner plumbing. Does sound like you had air in the system. mine did that too, but purged itself. (Air comes out when block gets hot but sucks coolant back in from the reservoir when it cools back down.)

Just don't let it get that hot again. Like the guys said before, you could warp your bank account.

If its air in the system you can try putting it on ramps and the service manual says rev it to 3000 RPMs 5 times and repeat if nesceesary

Think about it RPerry, if that were the case you'd only have interior heat when the block got too hot (Fine for Florida, not so good up here in the frigid north) The heater core is fed from the bottom center of the intake manifold at the front of the engine and returns to the block next to the water pump. The thermostat is on the other end and controls flow to the radiator hose only.