The lower the teeth on the pinion the cooler the motor will run. The higher the teeth on the pinion the hotter the motor will run.
If your motor is really hot drop a couple of teeth on the pinion and you will run lower temps.
If its almost untouchable your gearing is way to high, and the excessive heat will burn out the motor prematurely.
Try an 18t pinion and go up from there.
Original RC 10T, T4, RC8Te, Tekin RX8. Losi Ten SCTE, Slash 4x4.