As a side-bar to all of this fan checking, which I am saving for future reference, I would also suggest running the car, get it warm (operating temp) and then check your radiator to see if it is evenly hot. You may want to remove the fan shroud to help in this.
Some months ago someone discovered that the overheating problem was a plugged radiator core. This is of course after fans, Tstats, viscous clutches etc.
Also, if you do remove the shroud, you can carefully use a hose and reverse flush the radiator to help remove accumulated bugs and debris. Just be careful not to bend the soft aluminum radiator fins.
Also, minor point to check, but do the front electric fans actually turn? I had an old 240D and it got too hot. Did the whole fan, jumping etc but discovered the actually fan didn't turn. Kind of locked in a way. Weird, until I discovered that some mouse had built a next between the fan and the condensor. Removed and cleaned it and it started whirring right away.
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)