I had a '91 190E that ran in the same temp range. With a new radiator and thermostat the car still ran above 100C in the summer. I live in Palm Springs which is hotter than Phoenix. I came to the conclusion that the radiator just wasn't large enough. After all, when was the last time it hit 117F in Germany?
Anziani

'87 300E 205K
'95 E420 112K