When the engine was rebuilt, was the block cleaned? hot tanked, cooked, or washed? One could assume if it was cleaned at the shop it should be clean inside. Pulling a block drain plug will let you know pretty quick. If it is plugged, is there any way you can get a power washer wand to meet up with the drain and really blow through it?
It seems to me to be overheating really quickly, 4 to 5 miles? Mine isn't hardly warm by then. You sure the water pump impeller is good? Do you see water flowing in the radiator if you look down the filler hole? I would have to think even a poor radiator would make it 5 miles, the thermostat shouldn't hardly be open that quick. Something in the block is affecting water flow, maybe air pocket, wrong head gasket?
Joe
