All the Mercedes cars I have had show 90 to 100c when pulling a long grade (6 to 8 miles at 6 to 8 percent) even in winter.... Often with the AC on and out side temps from 100 to 118 F. I see it above 100c but never up into the red.. In general the thermostat does not really open until about 90.. So does run at about that on the long pulls in winter.. They do run at 80 or so down the road unless the out side temp is above 100 F then with the AC on even on the flats they run a little below the 100.. and a little below 80 on the 6 or 8 mile down hill grades in winter.. This is the way all the Mercedes I have had in the last 40 or so year have run.. 80 seems way to cool for a car that has an engine that is working hard.. I would worry about running that cool in the summer... I would for sure change the themorstat on one that ran that cool in summer..