Date registered: Oct 2012
Vehicle: 1972 220 D, 1974 450SL, 1995 E300D 2002 S430, 1976 300D, 1986 SDL, 1982 SD
Mentioned: 2 Post(s)
Quoted: 446 Post(s)
Revs are normal at that speed. Temp has more to do with coolant flow and air flow to heat exchangers. With AC off and heat on, you should see a goodly decrease in engine temp at the cluster.
I climb mountain passes at 75mph, and temp does not get above 185 on summer days, normally. When the system was not at its best, I did get much higher showings in the 210-redzone. Driving 75-80 for 250 miles did not make for much heat. Slowing down or climbing 6% grades did not show any effect either with a clean system.
This is for a 73, no AC, kept in good kip. YMMV