340 Overheat / Radiator Geyser

If the engine ran for 35 min...& there was no coolant flowing past the rad cap opening, it means the pump was not pumping...or the t'stat was jammed shut. Remove stat & test in boiling water. Check also there is nothing in the pump housing/t'stat housing that is stopping the stat from fully opening.

Make sure the impeller is NOT loose/spinning on the shaft.
Will-do