Originally posted by tkamiya
My 1994 E320 has the same engine as yours. On cool days with constant speed driving on highway, it levels off at 82C or so. In rush hour traffic, it goes to 102C or so.
Yup, mine is about the same. I have the same M104 motor found in your E320 in my C280, and mine is usually about 85 C or so when cruising... but will easily shoot up to 100 or so upon stopping after a long drive.
Only once did the temp ever get to 110, that was on a long ascending hill, doing 80 mph, with 3 passengers (4 people) including luggage, and a 100 F exterior temp. Anything above 110 and I'd worry a little!
Good luck. And of course, don't forget splitting the coolant/water mixture. You can even try 45/55, coolant to water, respectively, for a slightly lower operating temp.
NOTE: ONLY USE MERCEDES-BENZ COOLANT (from dealer, about $11)!!!