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Turn off auxillary water pump, residual flow? (archive)
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Posted by Patrick C 88 750iL on April 24, 2002 at 16:25:36:

Summer is approaching and my passenger side defroster slot is hot to the touch. This morning I inserted three thin wire-wrap wires into each of the three holes in the electrical connector above the two heater valve cores. Top wire reads 13.8V always unless I turned the Driver side temp dial to highest temperature (83F?), then wire dropped to zero V. Makes sense from comparing to Bentley electrical diagram. Lower Right wire (corresponds to passenger side) was 0.78V at low passenger-side temp settings, 13.8V at high temp settings. Same for the driver side.

At low voltage readings a current runs from the top connector through a solenoid coil to the lower connector, energizes the corresponding core and stop water flow.
The observation overall implies electical signals are available to the heater valves but the passenger-side core (new)is not stopping heated water from entering the heater core. Thus my case looks similar to what Grant posted in the attached link below, where a plunger inside the heater valve assembly was broken.

I want to remove the heater valve assembly and check on the plungers but don't know what I can find around the garage to plug the rubber hoses. I still need to drive the car to work. So for now I disconnected the auxillary water pump, the connector of which is on top and engine side of the valve assembly. While the car was running the passenger-side defroster was still a bit hotter than the driver-side defroster but not as hot to the touch as yesterday. I think I'll keep the disconnection until I can find some good plugs for removing the valve assembly.

How much water can still circulate the heater core when electrical power is removed from the aux water pump?

Patrick C 88 750iL


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