Amazing isn't it, how fast heat builds up when you start putting even just 200w into waste heat by stalling the motor. Ever put you hand on a 200w bulb? Imagine when you really stall a motor and make 500w into heat. This is why I got so hyped up on using the slower hubmotors. In my climate, heating the motor means it could take a really long time to cool.
The key thing to learn with your temp monitor is when you are pushing the motor hotter and hotter, and when you are in equilibrium with the cooling keeping up with the heating, so you can keep riding without getting hotter than the temp you decide is your max.
Below 200F is definitely well inside the safe zone. 250F is not guaranteed to ruin a motor, but by then you will see the color change of the windings varnish.
One thing to realize about a heated motor, is that stopping, which lessens the wind chill, actually causes a spike of more heat. That's when I've had some halls failures, after the ride is over. So if you are in the danger zone, some 15-20 mph cruising to let er cool can be a good thing.
Once hot, a mac will take longer to cool than a dd motor. On a dd, the metal outside is in direct contact with the magnets. The winding will cool slower, but at least it helps avoid magnet damage.
