Fleece Performance 03-07 Dodge 5.9L / 04.5-12 6.7L Cummins Coolant Bypass Kit (03-07 Manual Trans)Another product from Fleece Performance built out of necessity is the 2003 2013 Cummins Coolant Bypass kit. The Cummins engine cooling system was designed to adequately cool a 300 350hp engine. When the horsepower is increased there is an increased demand on the cooling system. The rear cylinders suffer from a lack of coolant flow, and therefore, experience the highest coolant temperatures. This can cause excessive pressure to build in the system,