CIM motors are quite robust thermally. However, they do heat up internally when loaded mechanically. The rate of heating increases as the loading increases.
Look
here for some details of how the motor's brush gear heats when loaded. Keep in mind that the thermal connection between the brushes and the motor leads is pretty direct; i.e., when the brushes get hot, the leads will also. Although the example load conditions covered in the link are worst case, the general trend is the same for all load conditions -- brush holders (and therefore leads) heat up much faster than the motor case.
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)