Yes, V8 has an auxiliary pump, located below the power steering fluid reservoir at the front left of the engine bay. The pump feeds the heater control valve.

Engine coolant temperature stays steady at 102C.

The air temperature grill on the IHKA seems clear. The ETK shows that there is also a temperature sensor in the heater core. So far I cannot find any way in ISTA to read the values of either sensor.

I'm going to go for another road test to see if I can hear any relay or flapper operating when the air goes from warm to cool.