What is the optimum engine temp (on the gauge)?

Just a little right of the center of the gauge is perfect.

100C IS SLIGHTLY HIGH BUT NOT TO BAD.POSS COOLING SYSTEM CK AND SERVICE

I have a 2003 CL 500. On the highway mine stays at 80c. on local roads it sometimes goes up to like 85/90c but stays under 100c. In the winter. Havent tried summer yet. The Official Operational Manual says "During Severe operating conditions and stop-go traffic, the coolant temp may rise close to 120c. The engine should not be operated with coolant temperature above 120c , doing so may cause engine damage....."