[GeeTwo]

It is interesting to note that (based on a number of posts on CD, not my own experience) that the damaging and performance robbing heat of a CIM is located on the rotor, not the stator or outer case.

The rest is my reasoning, not something proven through experience:

The rotor is only in significant thermal contact with the outer case at the bearings and somewhat less at the brushes; in each case the area of contact is limited or rapidly moving or both. There are also radiation and convection acting within the motor case.

Therefore, the most effective place to cool a CIM may prove to be conduction through the CIM output drive shaft. If your gearbox design allows it, you may wish to try cooling your CIMs by spraying their output shafts and pinions.

I am not familiar with anyone specifically trying to draw heat out through the drive shaft, but it should not be to difficult to design a heat sink that functions as its own fan and which could be attached to a CIM or mini-CIM when they are used in offset gearboxes.