75-82 is a normal running range. But, it should only go higher during long hills, stop-and-go traffic, and hot day's with A/C on high.

When it gets above 100*, it's time to back off, kill the A/C and let it cool down. If you let it go all the way to 120*, you are asking for trouble.

I'd recommend that everyone upgrade to the 9-blade plastic fan and smaller waterpump pulley. They can be bought new at the dealer or found on most late 83+ 300xD's.

I don't have A/C, but I have to work it pretty hard to break the 90* mark.