MuuMuu101's 68 Dart, A Learning Process...

mopowers said

If it got dry enough for the water pump to start rattling, there'd be a TON of water on the ground and it would have been a hell of a lot hotter than 160*.

I'd pull the top hose to make sure it has a thermostat, fix the leaky plug, fill it up with water and fire it up.

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The water temperature sending unit reads water temperature, not air temperature. That outlet flowing wide open would empty all the coolant in the system in very little time. 160 is probably what it was reading when the plug failed and the water left.

Regardless, with that kind of pressure loss there’s no telling what the localized temperatures got to in the engine.

The plug seems like a bad idea. Why not just install the heater hose nipple into the intake manifold and run a loop of heater hose over to it? That way you’re not dead ending that outlet and putting all the pressure on the plug. The heater hose should last as long as the radiator hoses, same stuff.