I rebuilt the 292 Y block in my 64 Ford pickup, it now overheats. I have checked the thermostat, it is working correctly. The radiator has been flushed. I confirmed the headgaskets are correctly installed. The timing is set at 5 degrees initial and the centrifigal seems to be coming in correctly. The radiator seems to have good flow when the thermostat opens but after a few minutes it starts getting bubbly then boils over. It will only idle for 15 to 20 minutes before overheating. The heads and block were both milled flat, little material was removed so the compression should not have changed much. The motor went together well, all the tollerances were in spec. The guage is only showing 185 degrees but a second thermometer is showing 200+.

Any tips would be appreciated. I was hoping I wouldn't have to take it apart again.

Confused.