Chevy 1500 6.5 turbo diesel, never overheated, until 1-inch hose from water pump to thermostat housing blew. Replaced hose, refilled radiator and pressurized. Now, it will overheat/pressurize very suddenly/quickly and then drops back to normal-back and forth-etc. Removed thermostat and hooked hose back up without the thermostat - no overheat probs. Put in new thermostat and overheat probs then re-appeared. No heavy white smoke, no oil in water, no water in oil. Usually has some black smoke at start, but clears. Heater also gets hot when overheating-then cold. All fluid level seem to stay @ good level. Any Ideas? Thanks much.

Sounds like air in the system.

How long did it run with no coolant with the busted hose? These ole oil burners don't like being hot.