Mishimoto Transmission Cooler - 03-09 Dodge Cummins 5.9L/6.7L

Thoroughbred Sku #: MIMMMTC-RAM-03SL
Manufacturer Sku #: MMTC-RAM-03SL

Item Options:




  • 2003 - 2009 Dodge Ram 2500
  • 2003 - 2009 Dodge Ram 3500

Product Details

Product Name: Mishimoto Transmission Cooler - 2003-2009 Dodge Cummins 5.9L/6.7L
Manufacturer: Mishimoto
Manufacturer Part #: MMTC-RAM-03SL
Thoroughbred Diesel Part #: MIMMMTC-RAM-03SL
Fitment Notes: 2003-2009 Dodge Cummins 5.9L/6.7L

There's no greater enemy for a transmission than heat. Whether your 2003–2009 Dodge Ram 5.9L/6.7L Cummins is a dedicated tow vehicle, hardworking fleet truck, or a daily driver with a liking for the drag-strip, you need to ensure that your transmission runs cool. Luckily, Mishimoto has developed a direct-fit transmission cooler to do just that. Our 2003-2009 Dodge Ram 5.9L/6.7L Cummins transmission cooler utilizes a stacked plate core for durable and powerful cooling. With a massive 212% greater core volume and 244% increase in fluid capacity, this trans cooler is a huge improvement over stock 2003-2009 Dodge Ram 5.9L / 6.7L Cummins transmission cooler.

The Mishimoto transmission cooler is not only larger than the stock cooler, but more reliable too. When the stock cooler's thermostat fails, it fails closed, bypassing the cooler and returning hot fluid to the transmission. Mishimoto has solved this common issue by making the thermostat in our 2003–2009 Dodge Ram Cummins transmission cooler fully serviceable and easily bypassed for constant cooling. A port located at the top of the cooler provides easy access to the thermostat for servicing in just a few minutes. Replacement thermostats can be purchased individually if needed; no more replacing the entire cooler if the thermostat fails. Owners in cold climates can still enjoy the fast warmup times that the thermostat provides, while owners in hot climates can choose to bypass the thermostat by replacing it with the supplied stainless-steel bypass plug.

To make this cooler even easier to install and service, Mishimoto saves you the hassle of removing seized fittings. The provided CNC-machined, stainless steel hose barb fittings let you cut to the chase, literally. These fittings and the supplied transmission cooler hose allow you to remove the quick-disconnect fittings and connect the stock soft-line to the Mishimoto cooler.

Like all Mishimoto products, this transmission cooler is backed up by our Lifetime Warranty with Accident Protection for worry free cooling as long as you own it.


  • Fits all 2003–2009 Dodge Ram 5.9L & 6.7L Cummins*
  • 212% Increase in core volume
  • 244% Increase in fluid capacity
  • Includes fully serviceable thermostat for fast warm-up in cold climates and thermostat bypass for constant cooling in hot climates
  • Stacked-plate design for tough and reliable cooling
  • Eliminates corrosion-prone quick-disconnect fittings
  • Mishimoto Lifetime Warranty

Item Options:


  • How much cooler will this keep my 05 cummins? In traffic my temps get close to 180 degrees and it gets me nervous. I have the 48re transmission and my stock cooler is leaking a small amount of fluid and would love a better one if i got to be getting in there anyway.

    Max Evans | 6/5/2019

    These coolers have twice the amount of core volume and twice the amount of cooling capacity so it will for sure help to cool the trans down as long as the condition of the fluid is good, filters are clean, and there isn’t a mechanical failure already involved.  Also, this fixes the problem of the thermostat failing closed that lets the coolant bypass.