Repair or upgrade the transmission cooling in your 1989-1993 Dodge 5.9L Diesel with Direct-Fit Transmission Coolers & Lines. The cooler lines are available in factory replacement or performance durable braided hoses with billet -AN fittings. The increase in fluid capacity and core volume will offer enhanced cooling efficiency with an aftermarket transmission cooler. Replace the problematic factory thermal bypass valve (if equipped) with a performance transmission cooler thermal bypass valve. There are many high-quality manufacturers accessible, including Dorman, BD-Power, Mishimoto, and others.