The cooler your automatic transmission runs, the longer it'll last. Car manufacturers know this. To dissipate heat from the automatic transmission fluid (ATF), they route transmission lines through a cooler that's either built into or in front of the radiator. Air enters through the grille and sweeps across the cooler or radiator's fins, helping cool the fluid.
Towing and hauling in particular can place extra demands on an automatic transmission. Most people have experienced "gear-hunting" as an automatic-equipped pickup or SUV toggles back and forth between gears while going up a steep hill. In scenarios like this, all vehicle fluids tend to heat up, and adding a load and/or trailer makes matters worse.
More Fins
Adding an aftermarket transmission cooler is one of the best performance upgrades that can be done to an extreme-duty automatic vehicle. Consider it cheap insurance against an expensive transmission rebuild.
When choosing an aftermarket cooler, apply the bigger-is-better rule of thumb: Select a unit that's rated at least three times more than the vehicle's GVWR (gross vehicle weight rating) or the largest model that will fit in an area of the vehicle that receives airflow.
Installation
Most transmission coolers come complete with all the fittings, plumbing and hardware necessary to do the job. Racing-application models often allow the buyer to furnish their own hardware, which can either be sourced at a good hardware store or in a separate trans-cooler mounting kit.
As mentioned, the cooler should be mounted where it'll receive airflow but be protected from rocks and other road projectiles. The instructions that came with the cooler shown here specify that it be mounted at least an inch from the fan, 1/8 inch from the radiator, two inches from the hood and/or wheelwells, and six inches from any exhaust component. Mounting the cooler on the same side of the engine as the trans-fluid return line makes plumbing easier. The Steps here show highlights of how to install an automatic transmission cooler.
