Heat kills motors and heat comes from current. Amp the motor out while it is running and see how much current it is drawing. If it is drawing above rated levels, the motor will definitely heat up (for example the bearings might be dragging, thus loading up the motor more than normal). I don’t know if there is a nameplate on the motor, but sometimes the manufacturer will give you enough info to calculate the current, if the current is not stated. For instance if they give you the HP and the voltage you can figure out how much current the motor should be drawing. 1Hp=746Watts, take the watts value for your motor and divide by the voltage 120V and that gives you the current you should be drawing. I do not have the NEC with me, and I am not sure how low they go (I believe mine is a 1/12 HP motor), but I believe the NEC has a chart in it that gives amp draw for various HP ratings.
I made a lot of assumptions here, but I hope this helps.