Originally Posted by Scott @ RA

Having track and road raced Z's more than probably anyone around..... I can tell you that honestly there is no need whatsoever for a differential cooler on about 98.9999% of the cars out there.... Unless you are doing endurance racing for 12+ hours on end, non stop, there is no need for a diff cooler. In fact, most of the time the differential will work better and rob less power from the drive train once the fluid is heated up to the operating temperatures.... I have NEVER seen a differential problem caused by over heating the fluid on these cars.

So to say a diff cooler is overkill would be a huge understatement. In most cases it would be counter productive as well as being just one other thing to have a problem with (leaky fittings, bad fan, bad relay, blown fuse, etc.) to be honest.