An older Gm4000/4100 will operate normally without any overheating problems with proper maintenance. Depending on conditions this could mean the air intake screen will need to be cleaned more often due to debris accumulation. More times than not the radiator itself is partially plugged so debris on the rear screen adds to the problem because the radiator cannot work efficiently.
There are still plenty of Gm4000/4100 operating perfectly in the field that do not have a reversing fan.
The Toro Company