The line wrench was catching on the thermostat housing as I turned the wrench left. I merely turned the wrench upside down so it wouldn't catch on the housing and the nut turned smooth as silk. I sprayed green label brake fluid on the supply line nut and the threads in the thermostat, wiped them off/out with a clean cloth then let them sit for a few minutes.

I'm going to start it up in a few minutes and post back here with updates.