My MM ESC gets hot

[suicideneil]

Not really. Part throttle driving is most likely to blame, therefore he needs a motor that is slower (lower kv rating) and will allow him to use much more throttle, without being too fast overall (which his current setup is). A lower kv motor on the same voltage and gearing as Linc suggested is ideal, or a mixture of lower kv and lower voltage- depends just how small this track is, but adding a fan to an overworked esc is never the best solution, when the real one is a change of setup. I/we only ever suggest fans for the MM when its being used outside of spec, that is, in a heavy MT or truggy and on 4s lipo- thats when the extra fan and a capacitor come into play.

Checking the wiring and gear mesh over is always a good idea though.