03-07 5.9L Dodge Cummins Coolant Bypass Kit


2003 – 2007 5.9L Dodge Cummins Coolant Bypass Kit


2003 – 2007 5.9L Dodge Cummins Coolant Bypass Kit

Multiple Options Available for Specific Application Fitment:

  • FPE-CLNTBYPS-CUMMINS-0305 (Default Image)
    • 2003 – 2005 5.9L With Automatic Transmission (1367)
    • 2006 – 2007 5.9L With Automatic Transmission (1368)
    • 2003 – 2007 5.9L With Manual Transmission (1369)

Increased Coolant Flow, Decreased Coolant Temperatures

The rear cylinders on the 5.9/6.7L Cummins suffer from a lack of coolant flow, and therefore, experience the highest coolant temperatures. This can cause excessive pressure to build in the cooling system, especially the rear of the block and blow out freeze plugs externally, or the smaller diameter plugs under the valve cover, leading to a failure. Our coolant bypass kit adds a secondary thermostat, that unlike other brands, works based on temperature instead of excessive pressure. This solves the problem before pressure becomes an issue by ensuring consistent temperatures across all six cylinders.


  1. Lowers coolant temperature at the rear cylinders
  2. Ensures consistent temperatures across all cylinders
  3. Prevents damaging coolant pressure build up
  4. Complete kit comes with braided hose and AN O-ring fittings to ensure a leak-free installation. Kits for 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.

Additional information

Weight 2 lbs
Select Model

2003-2005 W/Automatic Trans., 2006-2007 W/Automatic Trans., 2003-2007 W/Manual Trans.