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SKU #: FPE-CLNTBYPS-CUMMINS-67 Fleece Performance Coolant Bypass Kit 07.5-18 6.7L Ram Cummins

Purchase Fleece Performance Coolant Bypass Kit 07.5-18 6.7L Ram Cummins
    • 2003-2018 5.9L / 6.7L Dodge Cummins


Help eliminate the possibility of scored rear cylinders and blown freeze plugs with this Coolant Bypass Kit from Fleece! Increased Coolant Flow, Decreased Coolant Temperatures - The rear cylinders on ... read more

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Help eliminate the possibility of scored rear cylinders and blown freeze plugs with this Coolant Bypass Kit from Fleece!

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. Fleece's 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.

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.

  • 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 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 have a heat exchanger, a heater tube can be purchased at your local Chrysler Dealership [PN:68048997AA] to complete the installation.


  • ManufacturerFleece Performance Engineering
  • 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.
  • Kit includes billet hose brackets


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Rate Fleece Performance Coolant Bypass Kit 07.5-18 6.7L Ram Cummins

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Okay. Well today I'm typing up my review fo...
Okay. Well today I'm typing up my review for the recently purchased and installed Fleece Performance Coolant Bypass Kit. I purchased this for my 2006 Ram 3500 Megacab with the 5.9CR Cummins and the automatic transmission. First things first, DPP answered all my questions before my purchase and even gave me a phone call to confirm my vehicle information so I received the correct parts. Parts got to me in just a day or two so no complaints on shipping. Now onto the Fleece parts. Packaging was good to go and all the needed parts were included in the kit. The main bypass housing comes assembled with the new thermostat already installed and may I say they did an excellent job on machining. This thing is a beauty and it's sad that no one will ever see it due to its location. The new raised thermostat housing for the front of the engine is of the same quality as the rear assembly. The main bypass hose included is fitted with A/N fittings (as well are the 2 housings) and makes for a super clean and professional looking install. Now, since I have the automatic, my kit included a new delete pipe and plug for the factory plate heat exchanger for the transmission. This delete pipe seems to have started life as a factory one that was cut and welded closed. That's fine because it made for a perfect fit into the truck and still looks factory. Now if you managed to read this far the question most of you are wanting to know is, is it possible to do this while the engine is in the truck?? Well I am here to verify it is possible and really not that bad. This does however lead me to what should be a one star deduction because the instructions say ""1-2 hour install"".. Well since they did not specify if that was with the motor in our out of the truck, or automatic vs. manual, I have to let it slide. I am not a master mechanic but I'm not bad at it. This kit took roughly 6 hours by myself to install. The honest to god worst part to deal with is the removal of the factory plate heat exchanger hoses. OMG that was a PITA.. Now if you're a hose cutter then you can take 1-2 hours off my time because I like to keep my factory removed parts in good shape should there ever be reason to put them back on. The worst pipe is the one that crosses across the back of the head from the passenger side to the heat exchanger on the driver's side... I'm pretty sure that one pipe alone raised my blood pressure by about 50%. As for the removal of the freeze plug, it's harder to get to it than remove it. In my case I was able to drop out my down pipe and first straight section of exhaust to gain access. While it's a tight squeeze it wasn't too bad. A couple taps on the edge with a pry bar and it spun right out like they said it would. After that it was smooth sailing. Fit was perfect. For what it's worth I changed out my coolant at the same time (5 gallons total) and installed a new front thermostat (your factory one) and put in a new radiator cap. Seemed wise at the time. As for performance gains it didn't take anything of my 60' times and it didn't double my horse power, but I do notice it runs a bit cooler and my truck quit leaking out of the rear freeze plug (main reason I did this modification any ways). The only thing really missing from the kit would be some Loctite but every garage should have that so no big deal. In the end I am very impressed with quality and function of the kit. Install is possible but plan to remove a few things like inner fender wells and exhaust. Approved...
I just rebuilt my 07- 5.9, went overboard and...
I just rebuilt my 07- 5.9, went overboard and over budget. 4,000 miles after rebuild I blew rear freeze plug hitting 4,200 rpms, I was only there a few seconds, but a mile down road it blew out and lost all water. Choice was to drop tranny and transfer case to install new plug or spend money on fleece kit. I bought the fleece kit. It took 2 hours and I was done. Now engine runs a consistent tempetature no more 200+ than down. This is a great product. It's going in all of my other trucks.
Verified Buyer
High quality!
Great product, perfect fit!
Verified Buyer
i would buy if it would work on my truck
I would love to have this product on my truck but the mechanic was unable to install it would not fit the way it was designed
Verified Buyer
If you are pushing HP levels this is a necessity. Love the product.
Store Reply
Thank you for the review and glad you like the new coolant bypass kit. Definitely a great upgrade to ensure all six of your cylinders are getting proper cooling.
Verified Buyer
Works good
Verified Buyer
Installed on my 2015 Ram 3500 Mega Cab. Other than access to the rear freeze plug, (once you get it out you're home free) this works great. Peace of mind to keep the rear cylinders cooler. A must for any Cummins rig.
Store Reply
Thank you for the review. Agreed, that rear freeze plug is difficult to get easy access to, but as they say, the juice is worth the squeeze.

What temperature is the thermostat included in this kit? 180° or 195°??

Fleece has designed their coolant bypass kit with a secondary thermostat, So this would not replace your current temperature thermostat, rather it adds another to provide more equal coolant temps on the engine.


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Fleece Performance Coolant Bypass Kit 07.5-18 6.7L Ram Cummins

Fleece Performance Coolant Bypass Kit 07.5-18 6.7L Ram Cummins

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