I've been running a Ballistic 17.5 with a swapped stator for the last few months, and I'm having a weird gearing/timing/temperature anomoly.

The motor is under-geared and over-timed compared to the other racers at the track, but it still keeps up with the rest of them just fine. I wrestled with different gearing and timing configurations for a while until settling upon this one. The temperature though, seems to be steadily creeping upwards.

When I originally geared and timed it, it would reach 160 degrees after six minutes pretty regularly. Then it started dropping lower; 140 after 6 minutes, 160 after 20. Now it's on the rise again. Two weeks ago, it was 170 after 10 minutes. Last weekend it was 180 after 10 minutes. Same track layout, same overall conditions.

The motor doesn't seem to have lost any power, it just seems to be slowly getting hotter. Is this a slow failure of a motor due to mild overheating? Or is it just the result of environmental changes causing a confirmation bias?

I've found with my setups that there are a few things that directly affect the motor temp. Of course there are others, but these are the ones I look at first:

1. Ambient temperature
2. Track layout (when it is changed to something largely different than it was, the temp changes accordingly)
3. Rear tire foam (when the foams breakdown the temp goes up)

Make sure you have not overtightened the sensor board. It can make the motor run hotter.

A busted bearing causing drag on the driveline would get progressively worse run to run which would cause similar results to what you're describing.

I just replaced all of the transmission and axle bearings, but not the motor bearings, because they're difficult to replace.

I might have over-tightened the sensor cap; I'll give that a shot next time.

using brakes and/or drag brake makes a big difference in temps

I find if I am out front my motor comes off cool, I f I am trying to catch someone my motor is way hotter, regardless of the lap times

Replace the bearings. If you can't get them out then take it to an LHS that can. Cheaper than buying a new motor.