According to the website, the pictured kit is for 2007.5 through 2018 engines but Fleece has kits for other years as well.

There are a lot of upgrades you can do to your diesel to make it more powerful, more durable, and deliver more of whatever you need. But have you given much thought to any upgrades that will benefit an engine without increasing performance? Not many enthusiasts do, and I am here to tell you, reliability and maintenance are key factors to having a useful and long-lasting truck.

Take for instance the cooling system in your rig. We previously talked about choosing the right antifreeze, but have you ever considered adding something called a coolant bypass? I did some research about these to see what the hubbub was about and found the coolant bypass from Fleece Performance. I understand how it works, but I wondered why I might need one. That curiosity led me to reach out and ask why. I learned that if you drive a Cummins-powered rig, there is a definite need.

The easy part of the installation is placing the Fleece Performance bypass thermostat housing on the front of the engine.

It’s been proven that the rear cylinders on the 6.7-liter Cummins suffer from a lack of coolant flow. This can cause excessive pressure to build in the cooling system, especially at the rear of the block, and will likely blow out freeze plugs. Another area where you might see a plug vacate the block is under the valve cover. I don’t need to tell you how bad that can be.

The Fleece coolant bypass kit adds a secondary thermostat at the rear of the engine block, that, unlike other brands, works based on temperature instead of excessive pressure. This solves the flow problem before the pressure becomes an issue by ensuring consistent temperatures across all six cylinders.

According to Jeff Everett of Fleece, “one of the biggest issues on the 6.7-liter Cummins is the coolant flow problem to the rear cylinders. This can cause catastrophic failure or blowouts of the freeze plugs in an over-temperature/over-pressure condition. The Fleece Coolant Bypass kit is one of the most important additions you make to improve the reliability and longevity of the Cummins platform.”

The hardest part of the installation is removing the factory freeze plug at the rear of the engine and then installing the Fleece bypass housing with the additional thermostat. If I have any concerns about this system, it might be the need to access the additional thermostat should it ever need to be changed.

Finally, I wondered if this is something every Cummins owner should consider or if it is mainly for those engines that have been modified. “It is a benefit to all owners, and most popular among the towing and hot-shot customers that are seeing elevated engine load and coolant temperatures on a routine basis,” affirms Jeff.

Installing the bypass kit can be done by the home enthusiast, but it will require you have access to the rear of the engine This is accomplished by getting at it from underneath the truck. Once the rear of the engine is accessed, you need to remove the freeze plug found in the rear of the cylinder head above the transmission bellhousing. Once that is done, install the bypass thermostat housing and route the hoses to the front of the engine per the instructions.

Having a useful truck is not all about performance. If you don’t have a reliable rig, all the performance in the world will do nothing for you. Adding the Fleece bypass is an upgrade that will keep you on the road.