On my W210 I have pulled out the aux fans and replaced them with aftermarket fans that are thermostatically controlled (can also vary when they cut in). I am still running the OEM viscous fan at the moment, tempted to remove that fan and run a much larger fan on the back of the radiator as per more modern cars.

__________________
UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!