I did give it a tap with the hammer yesterday and no change. I'll check the interior temp sensor's dust level. I hadn't really gone into that one due to the fact that today the fan speed changed as the cold car became warm. Obviously with the monovalve unplugged and open, it was getting max heat from the core.
wonder how the coolant system would react to an acidic type flush. may try that next. Pretty sure when my I lent the car to my mother, the coolant light came on and she filled it with green coolant instead of water.

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg