Over 100C is normal in hot climates. The temp on MB thermostats is the temp at which they start to open. A lot of the time, as thermostat gets old, it starts to open at a lower temp.

If your temp is holding steady at 80C, you need to replace the thermostat. I replaced mine when I changed the coolant, and now it is back in the upper 80s to 100 range. Before I replaced it, the temp was running 82C on the highway.

Think about it, if MB thought that running 100C was not normal, then why did they design it so that a properly functioning thermostat should still be restricting coolant flow into the radiator at 100C? The fan clutch doesn't even start to pull mass air through the radiator until 95C.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record