-coolant temperature sensor replacement,
-with proper coolant mixture
-upper engine wire harness replacement
the temperature gauge is between 80+ and 100 °C (next white line after 80 mark) in my car .... usually ... in winter and summer.
Of course in theory the temperature can go to 120 °C and more, and in practice it can also rise to that value if there are such circimstances (staying in traffic during summer, etc.). I strongly believe that (bayhas will get mad with me) the "normal" temperature during driving the car is not more than 100 °C (summer). Indeed there is a statement in manuals that temperature gauge can reach the red marking; let's say 120 - 125 °C, but this is the upper upper upper limit, which is far away from normal and it is allowed only in special situations according to MB manuals. So logically is: if MB allows 120 °C then 100 is not so bad, we can say, but 120 is really a limit, not a reference for normal everyday driving.
In addition, rapid fluctuations of temperature gauge are also not ok one should say ... they indicate at some malfunctions (thermostate, viscous fan ...).
This is also interesting:
I experienced fluctuations of temperature gauge pointer over 85 °C. When it reached that temperature it usually jumped to 100 and more ...and then slowly (sometimes) dropped to 80+. I noticed some logic in these fluctuations with driving regime so I accepted it as a normal. I also studied this forum and noticed that this should be normal. I let the air out of the cooling system, etc. However the temperature fluctuations in addition to relatively high temperatures were still on. I got an idea (read about it on some another forum) and I tapped on the cluster display where the temperature gauge is and I noticed that the pointer jumps according to my taps. So it was not related to temperature changes but to something mechanical.
Solution: I removed the cluster, I removed the module where the temperature gauge is and I cleaned all contacts with contact cleaner spray, I also opened and cleaned the connector with 4 wires which comes into the cluster from behind (square shaped connector, the first on the left side of the cluster in direction of driving). The problem solved, relatively high temperatures and their fluctuations dissapeared.
Conclusion is that your high temperatures are maybe a result of bad contacts related to temperature gauge or the wires to it. when the car will be hot, test the situation with tapping onto cluster display over temperature gauge. if it will jump then you've got it.