Okay, mfr02 mentioned the motor "load" as being a possible cause for the heating up. That has me wondering if it's a drive line issue? Have you greased the drive line after running? I know a drive line without grease increases the friction between the flex cable and tube, resulting in an increase of drag and, consequently, heat from the motor working due to it's having to work harder. Following the path that mfr02 laid out, that means more current to the motor which, in turn heats up the ESC and shortens the run time due to pulling more amps from the batteries. If this is the case, lack of greasing, the service life the everything, tube, flex cable, motor and ESC will all be severely shortened. If the cable breaks, you could find yourself without a prop as well as it can and will pull the bottom of the shaft out and sink to the bottom of the pond