Living in Queensland, Australia we also get those fluctuations of temperature.

I run a small cooling fan for the motor of my Sea Commander and ensure that there is plenty of air movement throughout the boat. Additionally, simply by not running the motor for extended periods of time nothing gets overly hot.

As a matter of interest, how many use simple fuses to turn things off if there is an issue? Just out of curiosity.

Could be a number of things. Mis-matched ESC, Motor, and Prop is a big culprit in scale model boats where speed isn't an issue. Example, a small motor driving a big prop will cause the motor to overload = overheat.

Other causes could be excess friction possibly caused be the drive system (u-joints, shaft bearings, etc). Lack of lubrication, alignment, clearance...).

One guy had that problem last Sunday at the SSMBC meet. I should have taken a photo of the motor and Prop. A standard type 540 motor driving what looks to be a 3 inch 3-blade prop with at least a 45 degree pitch. Looks like he fried his ESC.

Lew