I believe that the PO would have told me if the fan clutch was misbehaving. I think he left it off after changing the belts thinking that it would help keep the car up to operating temperature this winter.

The way I understand the fan clutch works is that when the fluid (or semi fluid) inside gets hot (or warm), it expands enough to NOT allow the fan to freewheel. If the cluth was shot, then I should hear it freewheeling after every shut down. Is my logic correct?

I will try to get the car up to temperature and see if I get a repeat performance today.

No recognizable tune, very spooky though.

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1979 300D 275K