TxLaTx,
I think you are correct. The water exiting the thermostat housing, being heated by the engine, and not yet cooled by the radiator, would be the hottest. This would be the supply (sorry Red) for the heater. I had it backwards! From top of engine, through valve, through heater core and back into engine via waterpump (negative pressure side).
You can't keep a good Atomic down for long!
Stuart
