This probably isnít going to help you unfortunately, but Iím just blowing off some steam Ė Pun definitely intended. I have been having some cooling system frustrations during the last few days.
I discovered that on my car, a 1984 300D (California version, if it matters in this regard). There is NOT an auxiliary fan thermo-switch anywhere on the engine. The wiring diagram shows that the fan is activated ONLY by the switch on the A/C receiver-dryer. (via the relay, of course.)
O.K., Iím finally cooling off here. The 212 is degrees (boiling point in Fahrenheit). This is curious, as I would assume that it would be stamped with a Centigrade rating like the other one you mentioned (100 is the boiling point in Centigrade), but what do I know?
I just looked in my ANCIENT (circa 1983) parts book from SSF, and the part number listed as 005-545-03-24 is listed as: Thermo Time Switch / Coolant temperature sensor, 1 pole terminal, for ready to start indicator light at dash via preglow relay system. Used on 300D with OM617-912 engines up to #114041.
This part may have been superceded though, so beware of this fact. I see no listing for the other part number you listed, but this book is 18 years old.
Now, in retrospect, this was a pretty useless reply, wasnít it?