ferrofluid

[Parsons]

Hi guys have you used ferrofluid in you rear hub motor

 

[Raboa]

Is that fluid that comes from ferrets?

 

[danielrlee]

The following thread on Endless Sphere is the best source of information on the subject:

Definitive Tests on the Heating and Cooling of Hub Motors

Hey guys, so I've been meaning for a long, long time now to run a set of controlled lab experiments measuring the temperature rise of hub motors being subject to different load conditions. The main objective is to develop a more comprehensive 2nd order thermal model to incorporate into the...

endless-sphere.com

TL;DR - Ferrofluid is extremely effective on direct drive outrunner motors. Other motor types show limited to negligible benefit due to the increased airgap between the stator and motor casing.