A "friend" of mine wants to know; if you have wire that is too small in gauge going from the ESC to the motor, will that cause the ESC to run hotter?

(Also will the motor run hotter?)

I would have thought the increased resistance in the skinny wires would have mean less watts going to the motor, and hence less heat from the motor, but overall your 'engine cavity' may run hotter from all of the wires acting like heater elements.

No ...
take care,
  Dean P.

Ahh, but no to whom?

I would have thought the increased resistance in the skinny wires would have mean less watts going to the motor, and hence less heat from the motor, but overall your 'engine cavity' may run hotter from all of the wires acting like heater elements.

Only if you're not using a governor.  Use of a governor would, in this case, definitely lead to more hot air* because the governor (whether it's in the ESC or in the timer) would just crank up the throttle until the motor was up to speed.  You'd probably get a similar effect in an RC plane if the pilot is aiming for just the right speed rather than just nailing the throttle and boring holes in the sky.

* That's a joke, son.

I think a bigger heat contributor is where we run our system,, at what percentage,, my UNDERSTANDING, ( Tim correct me if wrong)
when we run our system at 50% rpm,, the excess current/voltage is turnied into heat as the ESC cycles to build the throttle signal?

Sorta right, sorta wrong.  The ESC cycles the voltage to the motor at part throttle (meaning the voltage at the motor terminals is either zero or very close to the battery voltage), but the excess isn't all turned to heat.  I couldn't quote exact numbers at you (among other things it depends on the motor construction), but I suspect that the system is only 5 to 10% less efficient at half throttle than it would be with half the battery voltage and running at full throttle.

The old "low frequency" ESC systems that were used back in the dark ages, when brushed motors roamed the earth and ate nickle-cadmium batteries for lunch, did burn up a lot of extra energy at part throttle.

Those thick wires are part of cooling,

Man, I hadn't thought about that -- yes, they are, aren't they!

(To the rest of you -- the motor and battery wires can be made to be in intimate thermal contact with the final drive transistors, which are the parts that need to dump heat.  Copper is one of the best heat conductors out there, so even with insulation in the way the wires would tend to draw heat out of the ESC where it can be radiated or conducted away.  If you're an ESC manufacturer and you really want to enhance this effect, you'd pick insulation with good thermal conductivity -- this is in the supplemental volume of the "Encyclopedia of Engineering" titled "crazy stuff".)

but I do not think it will be signifficantly worse if you use little thinner cables, however I found that many people install ESC reversed, means FETs (tha flar part f ESC) pressed to flat balsa surface. It should be istalled flat side exposed to air stream.

This will vary by ESC.  There are a lot of ways of getting heat out of components; the "modern" way with small surface-mount packages is to dump it into the PC board, and then get the heat out of that (possibly by the wires).  However, one can also glue heat sinks onto the tops of the FETs (I think this is what Castle does).  The best thing to do is what the manufacturer says to do.  If they don't, and if there's not an obvious heat sink, then the safest thing to do is to make sure there's airflow across top & bottom of the ESC.  If there is an obvious heat sink, then make the airflow go through that.

Personally, I just look at the ESC and say "where's the heat going?" But my background is a bit different from the average modeler.