Mishimoto: Transmission Cooler for ’03-’09 Ram with 5.9/6.7L Cummins

When the biggest enemy of your transmission is heat, you can have no greater ally than Mishimoto’s direct-fit transmission cooler. Designed for 2003–2009 Ram pickups with 5.9 or 6.7L Cummins engine, the MMTC-RAM-03SL cooler uses a stacked-plate core for 212% more core volume and a 244% increase in fluid capacity over stock.

Offering greater reliability in addition to increased size, this patent-pending transmission cooler solves the stock thermostat’s issue of failing closed, which causes hot fluid to be returned to the transmission. The Mishimoto thermostat is fully serviceable and easily bypassed for constant cooling—no more replacing the entire cooler if just the thermostat fails. In fact, owners in warm climates can bypass the thermostat completely by replacing it with the supplied stainless steel plug.

Note: Kit requires cutting of stock transmission cooler lines to remove the quick-disconnect fittings. Hose barb fittings included to splice the supplied transmission cooler line with the stock soft lines.


  • For 2003–2009 Ram 5.9L & 6.7L Cummins.
  • 212% increase in core volume.
  • 244% increase in fluid capacity.
  • 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.
  • Warranty: limited lifetime.
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