Do not forget, the '90+ cars received an updated fan blade for the M103s. I wish we could use the 603 Diesel style but the blades are the wrong direction.
Furthermore, M103s appear to 'run hot' compared to other MBs of this vintage due to the 87°C thermostat installed in them. Swap in a 79°C and the fan clutch will not fully engage nearly as often... did this a few years ago in my 300SEL and cannot be happier I did so.
Swap in the red aux fan switch on your '86 also.