[JRMichler]

Much better to put a temperature sensor in the windings. I've done motor durability testing, and we drilled a small hole into the steel stator (from the outside), then embedded a thermocouple. The temperature sensor should be as far into the steel as you can get. Ideally, it should be within 1/16" of the copper winding. In practice, within 1/4" should be good enough.

Google electrical insulation temperature rating to find the maximum allowable temperature.

And yes, you need a blower with enough pressure to push air through the motor. Computer fans are worthless for this. It needs to be a centrifugal blower. Try to take the inlet air from a high pressure area such as the bottom center of your front grille.