I was curious too about indicated temperature. My '85SD runs at about 85-90 in MOST circumstances. The exception was when I ran a stretch of freeway at 85-90 mph and it crept up to about 100.
Shall I assume that this is normal, and that the cooling system isn't sized to keep 85-90 at near full power output? In any case, there isn't much opportunity to run high speeds commuting to/from Detroit, where 65 mph is cause for jubilation!
'96 E300D 58k mi (wife's daily ride)
'95 Audi 90 118k mi
'92 GMC Suburban 138k mi
'85 300SD 230k mi (my daily ride)