I’ve previously covered the addition of the DiffsOnline LSD differential in Part IV, here I’ll discuss a custom cooling solution for the differential.
A track driven clutch type differential can easily reach temps in excess of 250 F without much effort. Running a differential hot reduces the life of the clutch packs, which can reduce lock up and lead to poor performance. The simple solution is running a finned aluminum differential cover, which BMW produced. But relying on air flow under the car to cool down a race rear end will only do so much and you can still expect hot temps. You also lose ground clearance, something I’d like to avoid when you may take the occasional off-track excursion.
The other solution is an external cooler. BimmerWorld produces a kit for this, which is fairly universal. The GTS E36 build I picked up a while back came with boxes of parts, one being a mostly complete differential cooler. It’s a pretty simple setup; a self priming pump to draw fluid from the differential, a heat exchanger, a fan, and various fittings and hose.
I placed the cooler at the rear of the spare tire well, mounted on some fabricated aluminum mounts I made from angle stock. I also used rubber idolater mounts from McMaster Carr to contend with vibrations.
The lines run through the sheetmetal using AN bulkhead fittings. The setup was pretty compact because I was also mounting my cooling shirt cooler in the spare tire well. Because of these constraints I had to try a few different AN hose ends to get the angles just right.
Eventually I came up with the right combination and was able to have everything fit nicely. Under the car, the braided stainless lines run to the differential cover. The drain and fill plug were replaced with AN adapters from Setrab.
The completed setup:
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