Protect your 1998.5–2002 Dodge Ram 2500/3500 5.9L Cummins from overheating and pressure-related failures with the Fleece Performance Coolant Bypass Kit. The rear cylinders on the 5.9L Cummins are known for poor coolant flow, leading to higher temps, excessive system pressure, and the risk of blown freeze plugs—especially in high horsepower, towing, or heavy-use trucks.

This kit features a secondary thermostat that activates based on coolant temperature, not just pressure, ensuring even cooling across all six cylinders and preventing dangerous pressure spikes before they start. The complete kit includes a premium stainless steel braided hose for maximum durability, AN O-ring fittings for a leak-free install, and all necessary hardware for a secure, professional fit.

The Fleece Coolant Bypass Kit is a must-have upgrade for any diesel owner looking to safeguard their 5.9L Cummins, boost reliability, and keep their truck running strong under any load or conditions—now with the added strength and longevity of stainless steel braided lines.

Benefits:

• Lowers coolant temperature at the rear cylinders
• Ensures consistent temperatures across all cylinders
• Prevents damaging coolant pressure build up
• Complete kit comes with braided hose and AN O-ring fittings to ensure a leak-free installation.
• Kits for MY 2003+ include billet hose brackets.

Why do I need a Fleece Coolant Bypass?
One of the biggest issues on the 5.9/6.7L Cummins is the coolant flow problem to the rear cylinders. This can cause catastrophic failure or blow outs of the freeze plugs in an over-temperature / over-pressure condition. The Fleece Coolant Bypass is one of the most important additions you make to improve the reliability and longevity of the Cummins platform.
Application Notes:

• The 2003 - 2007 5.9L automatic transmission version will eliminate the factory transmission fluid heat exchanger. The heat exchanger is designed for use in cold climates to warm the transmission fluid with the engine coolant. It is not necessary for use in warm climates or high horsepower applications, nor does it detrimentally affect the trucks performance when removed.
• For model years 2007 - 2018 6.7L trucks, including both automatic and manual equipped transmissions, factory installed transmission fluid heat exchangers are uncommon. For customers with a 6.7L that has a heat exchanger, a heater tube can be purchased at your local Chrysler Dealership [PN:68048997AA] to complete the installation.