Is the hose from the reservior to the overflow tank in the fender intact? You will have to remove the fender cowling to be sure, but that's only about 6 screws. I didn't think it to be anything but cosmetic/neatness until I replaced the hose. Ran at 90-110 prior and stays at 82-84 since.
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)