Harrell,
I'm with the air-locked thermostat idea. Check out this recent thread on the subject:
"Water not circulating" One thing that helped us was the Infra-red thermometer. You can use it to quickly check the engine temp below the thermostat housing and above the thermostat housing. If the block reads 170 with a 160 thermostat in (or 180/190 with a 180 thermostat in), BUT the radiator and the upper hose are not nearly as hot, THEN the water is not circulating through the thermostat.
The hole in the flange of the thermostat housing is a good idea, just keep in mind that the hole can get plugged up with stop-leak too, and you can still get air locked.
Hope this helps. Post your results!
-Michael
