95 104: Viscous or T-Stat problem?

[haasman]

After doing a lot of searching on this site, I am still unsure which is needed-

The 95 E320 wagon temp goes above 100c and can see 110c going up a hill on the highway with an example today’s 103f outside temperature.

At one point the AC stopped working. I stopped, waited and then started up again and the AC returned.

Going down hills I see less than 100c engine temps, going up hills higher than. With the AC off it will generally display less than 100c, whether stop and go or highway.

The coolant is MBZ and it has a –10f mixture, the viscous clutch does work on the fan, I can hear the roar and with the AC on the aux fans both are running. The engine has 10w-40 oil. The car has 97k miles on it.

Is this a viscous coupling problem or a thermostat problem?

Thanks in advance,

Haasman