Can someone confirm that the black tube on the back of the block is the one supplying coolant to the pump. This is also where the heater return pipe connects. What's driving me nuts is that the thermostat *appears* to have it's temperature sensing side on the *downstream* side, toward the pump inlet. If true, how the heck does the thermostat get heated so that it opens?

I'm asking this because the engine is going into a one-off (in sig.) The coolant pipe heading to the radiator, the one I thought was the pressure side, wasn't. It's not a big deal but I'd like to know what direction coolant flows in the system. Couldn't find it in Helms.