If it's any help or consolation, they're pretty much ALL "on or off" heater control valves. I wish they'd regulate as well as the one in my 740...
The very late model year ones (92-93) seem to work much better - I don't know if this is because of a design change or just that they're younger.
Good luck and I hope you have no leaking heater core.
Have a pressure test done on the cooling system with the heater valve fully open- that ought to confirm a leak.
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Rob Bareiss, New London, CT 86 244, 87 244, 88 744
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