After 4K miles in the 560 I find 80-82*C to be the norm in temps up to 100*F. You need to get a coolant mixture tester, like $2 at the local Pep-Boys. Like Jim suggested aim for a 40-45% coolant to 55-60% water mix, and a bottle of water wetter (I run 45/55 on the 560).
Also check that hose that Earl suggested.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.