All motors are different, which might sound obvious, but a windscreen wiper motor has been designed to wipe windscreens on cars.
So, they have to deliver high torque, and have to be compact, so as not to impact on the "look" of the car. On the up side, it's pretty easy to have them sited in a high flow air-stream.
A compact high power motor is always going to get hotter than a large heavy one. For the same number of wire turns, the wire can be thicker and the magnets stronger. Weaker magnets means more current required, and thinner wire means more heat for that current.
One way to fix it, is to attach your new saw to the front of your car, and drive around whilst sawing. That way you would get the required airflow.
A more practical solution would be a bigger motor, or different/better gearing.
I suspect you won't achieve cooling equivalent to the automotive environment with a practical fan setup.
Edited By Andy Ash on 16/04/2017 17:49:16