Thanks for the responses.

I tried once again to loosen the thermostat housing after soaking with penetrant... no luck, and I really was concerned that those studs could be easy to break.

I turned to my torch and was going to try the candle wax trick on it. As I was heating the lower nut I heard gurgling and when I checked the reservoir had emptied.

Evidently the heat from the torch had warmed the housing enough to cause the thermostat to open and allow the coolant to flow into the block. Thinking about it I would guess a heat gun directed at the housing would have rendered the same results.

Randy