blacky

A while back we had a thread where the engine was able to operate without a water pump. At about 20 mi (20 min) on the highway the temperature was roughly 220 F. The water pump wasn't working because the water pump chain was broken.

How could this have been?

The only explanation I have is the thermo-siphon effect.

Flow would be backwards from normal.

1. Cold coolant flows from lower radiator through open thermostat into engine.

2. Coolant rises through engine by convection as it is heated.

3. Hot coolant flows from top of engine to upper radiator. Meantime cold coolant continues to flow from lower radiator into engine through open thermostat.

OP observed flow through upper radiator hose. If this flow was backwards, from engine to radiator, then this observation would support the thermo-siphon hypothesis.