Too much heat will kill any transmission, no matter how good the internal parts may be. Whether you are cruising, crawling, dragging, playing in the dirt, or towing big toys, your transmission is creating friction and heat, and it's relying on the fluid for lubrication and cooling. Modern trucks include radiator-mounted transmission fluid to water-cooling tanks, and these are rarely adequate for the rigors of our favorite activities. Some towing packages include an auxiliary transmission oil cooler, but for those of you unwilling to leave your transmission at the mercy of factory parts, we'll show you how to install an aftermarket cooler. First, let's look at the three main types of transmission coolers available: fin and tube, stacked plate, and fin and plate.
Fin and Tube
The most traditional design uses a single tube to move fluid from one end of the cooler to the other. While in transit, the transmission oil passes by fins that transfer heat away from the fluid. This design works, but has the least amount of surface area in contact with the hot oil.
Stacked Plate
This is the most compact and durable type of fluid cooler. It is constructed out of multiple flat "tubes" (plates) with ridges to increase the surface area. Oil is cooled by air flowing through stacks of these plates. Since these coolers don't have fragile fins that can be bent, they are ideal for use on trucks that get hit with high-speed debris during bad weather and off-road adventures.
 The B&M Hi-Tek fin and plate...  The B&M Hi-Tek fin and plate cooler comes with a 12-volt electric fan that turns on whenever the fluid temperature reaches 175 degrees Fahrenheit. We used some of the factory cooler lines but also needed a little extra 3/8-inch line to complete the project. |  Once the truck was in the...  Once the truck was in the air, we drained the transmission pan. It seemed like a good time to do a fluid change while the truck was off the ground. |  The torque converter in our...  The torque converter in our Dodge had a removable drain plug, a convenient feature seeing as diesel converters can hold seven (or more) quarts of fluid. |
 The B&M Hi-Tek Cooler came...  The B&M Hi-Tek Cooler came with NPT female threads, we chose to plumb everything with a 3/8-inch hose barb. |  Using self-tapping sheetmetal...  Using self-tapping sheetmetal screws, we positioned the cooler opposite the radiator above the lower valence. Be sure to locate the cooler in a place where you can still make use of the factory cooling lines. |  The new 3/8-inch line was...  The new 3/8-inch line was installed between the original cooler "in" and the new cooler "out." |