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, especially the rear of the block and possibly blow out freeze plugs externally, or the smaller diameter plugs under the valve cover, leading to a failure. Weve designed our coolant bypass kit with 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.