Update:

I swapped sensors from my other 617.952 car that runs perfectly with no difference.

I then swapped the thermostats, and voile! It was that stinking thermostat all along! I even replaced it with one from worldpac two years ago when I first realized I had a problem. The new one from the mb dealer that I put in the donor car now runs hotter too...but it's a steady 90-95C instead of the 100+ creep I was experiencing with the other car.

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)