O.K, I'll chime in here because I too have one, a 1982 240D automatic that I load up and drive all across the Southwest and yes, @ 60 ~ 65 MPH it gets up to 90* C with four people in the car and the AC on .

You're in New Mexico so that's not running terribly hot .

Failing to flush the entire cooling system is a fools errand because there is always accumulated silt & sediment in the block .

It's easier to flush everything at once too, far easier than removing the radiator for separate flushing .

We just came back from Nevada where we had some 113* days, then the temp gauge got up to 100* C but no higher and cooled back down rapidly once parked in the shade .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better