Cooling your 48re transmission might be a challenge for some if you live in a warm climate or use your truck for a lot of heavy hauling or towing. If your truck deals with higher than average transmission temps, it’s recommended to add a transmission cooler to your truck.
We did an in depth write up about the Best Cummins Transmission Coolers, and for your 3rd gen Cummins, the Mishimoto MMTC RAM-03SL is hands down the best 48re transmission cooler upgrade due to its direct fit and serious cooling capabilities.
If you are looking for a lower cost alternative, look no further than the Tru Cool 40k. The Tru Cool 40k is our recommended transmission cooler for most heavy duty applications, so fits the bill when it comes to keeping your 48re cool.
Product
Direct Fit
Price
Buy
Mishimoto MMTC-RAM-03SL
$558.77
Mishimoto MMTC-RAM-03SL Specs
Like many Mishimoto transmission coolers, the MMTC-RAM-03SL is specifically designed for the 03-09 5.9L and 6.7L Cummins. this cooler is a direct fit application that requires little effort installing. The cooler features a 244% increase in fluid capacity over the factory setup and a 212% increase in total core volume.
Cooler Dimensions: 26″ x 10.94″ x 0.87″
Cooling Rows: 48
Fluid Capacity Increase: 0.88 quarts
Fitting Type: 3/4″-16 SAE Barb
Installation Kit: transmission hose, fittings, worm clamps, thermostat bypass
- DIRECT-FIT UPGRADE FOR 2003–2009 DODGE RAM CUMMINS – Engineered as a bolt-in replacement for Dodge Ram 2500, 3500, 4500, and 5500 trucks equipped with 5.9L or 6.7L Cummins diesel engines and 47RE, 48RE, or 68RFE transmissions
- MASSIVE COOLING PERFORMANCE GAINS – Stacked-plate core delivers a 212% increase in core volume and a 244% increase in fluid capacity over the stock transmission cooler, dramatically reducing heat buildup under hard towing
- FULLY SERVICEABLE THERMOSTAT WITH BYPASS – Unlike the OEM cooler where a failed thermostat locks closed and routes hot fluid back to the transmission
- ELIMINATES PROBLEMATIC QUICK-DISCONNECT FITTINGS – CNC-machined stainless-steel hose barb fittings replace corrosion-prone OEM quick-disconnect fittings that are notorious for seizing on high-mileage trucks
- PATENTED DESIGN BUILT FOR WORKING TRUCKS – Features a robust 48-row stacked-plate core with a 26" x 10.94" x 0.87" footprint
Tru Cool 40k Specs
As we’ve discussed a number of times, the Tru Cool 40k is head and shoulders above other universal transmission coolers in the heavy duty use department.
Sure there are other transmission coolers that might be larger or include a fan, but for the cost, consistent performance, and simplicity, it’s hard to go against the Tru Cool 40k for the money for any 48re application.
Cooler Dimensions: 8 1/2″ x 22″ x 1 1/4″
GVW: 40,000 pounds
BTU Rating: 45,000
Fitting Size: 3/8″ inverted flare hex with 5/8″ thread size – This is great for those looking to install custom transmission lines
Installation Kit: Yes – Includes universal installation kit with rubber transmission line, various fittings, clamps, and mounting hardware
After 15+ years in the automotive industry, I’ve developed strong opinions about transmission cooling — and about the lack of reliable information available to enthusiasts who actually need it.
I’ve built and developed transmission cooler systems across a wide range of applications: street cars, race cars, and trucks. I created this site to put what I know in one place.
If you’re an automotive enthusiast trying to make a smart decision about your transmission and its cooling needs, this is the resource I wish had existed when I was starting out.
