Radiator

[Carls_jeep]

Rivet, flapper are the same to me. They restrict water flow and need to be removed. The purpose of the hole is to vent air from the block and anything in the way is not good. The hole has been open since the advent of the thermostat and the rivet/flapper is a recent addition that is not needed and could possibly retard the elimination of air. Once the thermostat has opened the hole serves no purpose.

[Birddog7]

Carlsjeep, You are 100% correct. I got to thinking and looking again at the thermostat. That rivet/flapper does block the the air from venting. When engine starts the air pressure closes that little flapper so I would have the same problem. So I drilled a 1/8 inch hole in the side plate of the thermostat and reinstalled it. It ran at 165 to 175 degrees and no overflow seem to be operating normally. 
Now on to a alternator/electrical problem. Thanks everyone for your help especially Carlsjeep.