The factory transmission oil cooler on your 2003-2007 Dodge Ram 5.9L Cummins is a liquid-to-liquid cooling unit, utilizing the engine's cooling system to cool the transmission fluid during warm outside temperatures and warm the fluid during cold outside temperatures. This design is tried and true, and it works. Until it doesn't. When they wear out and fail, it can leak coolant into your transmission fluid. Mixing coolant into your transmission fluid can have catastrophic results, and nobody wants to spend thousands of dollars to rebuild or replace their transmission if it can be avoided. The Mishimoto Replacement Transmission Oil Cooler is a direct fit, OEM replacement that requires no modification to install. Made to OEM specifications, this transmission oil cooler is equivalent to an OEM part. By replacing your transmission cooler preventatively, you can save your transmission from falling victim to premature failure. As with all of our products, this cooler is backed by our signature Mishimoto Lifetime Warranty.