I have to agree with the use of a motor cooler being only good for the initial part of your race as my experience also showed that the motor still hit the same temps at the end of the run.
More recently I have ditched the motor cooler and fans on the motor and am finding performance no different. I think its best to understand the temps of your motor (brushed or brushless) and how gearing affects this.
Coolers and fans could skew these results and could possibly lead to a situation where your fan dies mid-run and all of a sudden your motor hits its threshold temp and burns out
Fans also add weight to your car