Is everything stock? My 400X and a few friends' have had no problems at all with well over 200 flights on mine. I live in SC and it has been flown in 30 to 105 degree weather without ever overheating.

Where do you have the ESC positioned? My layout has the receiver cut into in the nose, the battery at the front of the tray, ESC with velcro next, and the the motor wire-tied to its tray. The ESC is just velcroed in and doesn't ever get hot. Is your ESC covered?

How long are your overall flight times? Mine gets 7 - 10 minutes max at full throttle. If your overall is less than that, the motor may have a problem and is drawing excessive current. Was the battery hot also? If not, the problem is probably the ESC. If so, it might be the motor...

Good luck....