Thanks, it does make sense that there is a path to allow the coolant to return past the heater.

I suspect the water pump pressured hot coolant flow comes from the back driver side of the block/head up to the 'T' for the windshield washer reservoir and continues on to the split on the hose near the brake booster. One side of this split, as you said is a by-pass that returns to the monovalve by the battery. The other side flows through the heater when the monovalve is opened by the climate control to control the flow by pulsing the monovalve solenoid. This hose is 124 830 5515 according to the EPC. Haven't installed it yet due to not knowing if the master cylinder and the brake power booster must be removed first.

If this is true then the flow control solenoid can't block the ' by-pass ' input return. So the molded part of the monovalve must allow a constant flow of the ' by-pass ' coolant to return to the water pump. The monovalve electric pump would suck coolant from the heater and return it with the by-pass coolant back to the water pump.

Also, if this is true. the small 90 degree hose from the windshield washer reservoir would be coolant that flows back to the monovalve and joins with that return flow to the waterpump. This flow is blocked by the thermostat in the bottom of the reservoir based on the washer fluid temperture.

At least that is how I think it works at this time. I plan to find a junk monovalve to check out the flow inside the monovalve.

I've read a few mentions that this flow must be maintained to provide for additional cooling of the back part of the head/block.

This, to me, is a really smart design and allows good computer control of cabin temperature.