I have a 1981 300d and just the other week i had the Radiator flushed and a new temp sensor put in. The question that I have is what is the noraml operational temperature of the car. Mine is like right in the middle of the temp gauge on the dash, is this correct. and another thing I just changed my oil the other day with 15-40w. Well when it seem the engine gets hot I sort of lose oil pressure at idle it goes down to the 2 on the oil pressure gauge on the dash. My question is, is this normal.

Under most conditions the normal temperature is in the 80-90C range.

The oil pressure of 2 bars is normal for hot idle. It should be pinned at 3 bar whenever you are above about 1500 rpm (hot), and whenever the engine is cold.

More specifically, I'd expect the pointer to be right at 82*C at idle and easy cruising. If you took the grapevine northbound flat out, I wouldn't expect more than 105*C at Tejon Pass. Maybe 110*C if you had the AC running.

New radiator and temp sensor... what about the thermostat?

Sixto
87 300D

All that I had done was the Radiator flushed, new temp sensor, and new thermostat. I still have the original radiator.