Secondary Derale Transmission Cooler

Jacob Szymanski · August 15, 2022

I noticed my transmission temperature getting quite high when driving on trails or towing through traffic so I decided to add a secondary Derale 13900 transmission cooler in addition to the stock front mounted cooler. My truck is a 2020 Custom TB with the 5.3 and 6 speed 6l80e. This kit came with everything I needed except for a couple fittings, and the fan is wired to an ignition power source so it won't drain the battery. You can see that it is mounted to a winch mount that I had made, but without the winch there that would be a great spot to fit the cooler. Essentially I followed the return cooler line from the transmission forward until the hard lines split off into two rubber lines with the return going to the driver side of the truck. NOTE: The hard lines are 3/8" but the rubber line is 1/2" (learned that the hard way). I first held the cooler in place and measured what angle it needed to sit at and tacked together some mounts, then after a couple of iterations got it to where it fit and the skid plate did not interfere. I then finish welded, drilled, tapped, and painted the mounts. On the cooler itself, I mounted the 180 deg thermostat to the lower connection. With the cooler location determined, I then measured and cut the 3/8" rubber hose in the kit. I then clamped the return rubber line on the truck, cut the rubber hose, and connected the 3/8" cooler hoses to the pre-existing 1/2" hose on the truck. I used one 3/8-1/2 straight barbed connector and one 3/8-1/2 90 deg barbed connector. Some zip ties to tidy up the lines too. Wiring was simple as well, easiest way to get a for sure ignition power source was to get a fuse tap from autozone for a micro2 fuse and then you have a fused ignition source. Ran the power to the thermostat and then positive from motor to the other side of thermostat and the ground to the frame. The hole in the skid plate has an aluminum mesh behind it to keep small rocks out, and it's pretty high up so shouldn't see much abuse. Haven't given it a full test for cooling capability yet but the fan is nice and strong so I have no doubt it'll help. For about $200 total I'd say its a great upgrade for anyone who tows in the city or hits the trails on any steeper terrain.

Jacob Szymanski · August 15, 2022

Forgot to add, but also had to refill the transmission obviously. Make sure it's nice and level and get a fluid pump but it was quite an easy process that is published readily for the 6l80e.