Unless you're experiencing sub-arctic conditions in Maryland, 75C to 37C is a massive delta. You've got a flow restriction. What brand is your thermostat? I bet it's aftermarket.

That's the first place I'd look.

ETA: checked my notes. Typical rad delta should be 10-15C. You're hovering around 40C. Re: aftermarket thermostats, a pot of boiling water is a dramatically different environment to a thermostat housing in a running vehicle. The reasons why are pretty intuitive. Spring force is just one of several key variables. Get a Behr or Wahler and good luck.

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1981 240D 4sp manual. Ivory White.