Theres your problem,

its a BEHR fan clutch which is trash. They came original in the W124 body E300D and are completely hopeless, the fan catches at 90C coolant temperature and cuts out below 90, the E300D has a 95C thermostat, so the fan is always locked.

As vstech said, the 98 model with the 11 blade fan wheel is a far better upgrade.

Before you do anything to change the fan clutch, take an air compressor and blow out the radiator and condenser fins. The clutch needs a lot of hot air to work, clogged fins will not allow air to pass.

btw - is your old clutch wobbly or scratchy to turn?

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)