Have you reverse-flushed the engine? If not, then the contaminates in the water jacket will seriously aggrivate the overheating.
Let the motor cool, then remove the upper and lower radiator hoses, and the thermostat. Stick a garden hose where the radiator hose attaches to the water pump. Turn the hose on, and you'll be amazed what kind of crud comes out of the thermostat housing. Let the hose run till clean water runs out of the thermostat housing. That will eliminate the possibility of crap in the water jacket causing the overheating. Buy a new 160 degree thermostat, and drill a 1/16" hole through the flat part of it. Refill with 1 gallon of antifreeze and fill the rest of the way with water. Let us know what happens.
Chip
