I had a similar issue with my 190e a few years ago and culprit was the temp sensor. The aux fan is supposed to come on at 105 and would never come on causing high temperatures in stop & go traffic. I replaced the fan clutch & radiator with no success. Finally after I replaced the $24 sensor everything was fine.

smk_texas
93 400e - with Kumho tires 16 months old (very pleased)
99 Merc Villager