If you own a Cummins-powered Ram, you know the rear cylinders can run dangerously hot, leading to cracked heads or blown head gaskets. A coolant bypass kit reroutes flow to solve this weak spot, protecting your engine and improving reliability.
This guide reviews the best kits on the market, covering fitment for 5.9L and 6.7L engines across model years, materials, and installation ease. Whether you are a weekend wrench or a full-time hauler, you will find the right kit to keep your truck running cool.
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Fleece Performance – 13-18 RAM 2500/3500 6.7L Cummins Coolant Bypass Kit (F…
Best for2013-2018 Ram 6.7L owners
- Direct replacement fit
- Quality materials
ConsiderLimited to 13-18 models
Coolant Bypass Kit Compatible with Dodge Ram 6.7L 2007.5-2018 for Cummins D…
Best forVersatile 5.9/6.7L fitment
- Corrosion-resistant anodized finish
- Fits manual and auto
ConsiderInstallation may need expertise
Fleece Performance – 2019+ Ram 2500/3500 Cummins 6.7L Coolant Bypass Kit (F…
Best for2019+ Ram 6.7L trucks
- Direct fit for 2019+
- Quality construction
ConsiderOnly for 2019+ models
Fleece Performance – 07.5-12 Dodge/RAM 2500/3500 6.7L Cummins Coolant Bypas…
Best for2007.5-2012 6.7L trucks
- Exact fit for 07.5-12
- Durable materials
ConsiderLimited model years
Fleece Performance Engineering FPE-CLNTBYPS-CUMMINS-0305 Coolant Bypass Kit…
Best for2003-05 5.9L auto trucks
- Leak-free AN fittings
- Braided hose included
ConsiderAuto trans only
Coolant Bypass Kit with Nylon Braided Hose Perfectly Compatible with 2007.5…
Best forBudget-friendly broad fitment
- Nylon braided hose
- Wide compatibility
ConsiderProfessional install recommended
Frailys Coolant Bypass Kit for 2007.5-2018 Ram 6.7L & 2003-2007 Ram 5.9L Cu…
Best forTemperature reduction priority
- Reduces rear cylinder temp
- Leak-proof AN connectors
ConsiderNewer brand
Fleece Performance Engineering FPE-CLNTBYPS-CUMMINS-VP Coolant Bypass Kit C…
Best for1998.5-2002 5.9L VP trucks
- Leak-free fittings
- Braided hose
ConsiderOnly for VP engines
Coolant Bypass Kit Compatible with 2007.5-2018 Dodge Ram 2500-5500 Cummins …
Best forNo-frills essential protection
- Anodized finish
- Consistent temps
ConsiderGeneric brand
12V Coolant Bypass Kit (1994-1998) w Stainless Steel Braided Line
Best for1994-98 12V Cummins
- Stainless braided line
- Quality materials
ConsiderLimited to 12V engines
Fleece Performance 13-18 6.7L Coolant Bypass Kit – Precision Fit
Brand: Fleece Performance Engineering
A precise, durable kit for late-model 6.7L Cummins trucks.
This Fleece Performance kit is engineered specifically for 2013-2018 Ram 2500/3500 trucks with the 6.7L Cummins. It is a direct replacement part, meaning you can swap it in without modifying your cooling system. The quality materials ensure long-term durability, even under heavy towing conditions.
You will appreciate how the kit is designed to fit your vehicle perfectly, eliminating guesswork during installation. It addresses the rear cylinder hot spots that plague these engines, helping you avoid costly repairs. If you want a reliable, vehicle-specific solution, this kit delivers.
- Direct replacement fit
- Quality materials
- Vehicle-specific design
- Limited to 13-18 models
- Price not listed
LAIKOU Coolant Bypass Kit – Anodized Aluminum for 5.9/6.7L
Brand: LAIKOU
A durable, multi-application kit that protects your Cummins from hot spots.
LAIKOU’s kit is built from premium aluminum and solid steel with a black anodized surface, giving you excellent corrosion and oxidation resistance. It fits 2003-2007 5.9L manual transmission trucks and 2007.5-2018 6.7L models with either transmission. This broad coverage makes it a versatile choice for many Ram owners.
The kit solves the classic coolant flow problem to the rear cylinders, which can cause catastrophic failure if left unchecked. By lowering coolant temperature at the rear, it helps maintain consistent engine temps. The high-quality AN fittings ensure a leak-free connection, so you can install with confidence.
- Corrosion-resistant anodized finish
- Fits manual and auto
- Prevents rear cylinder overheating
- Installation may need expertise
- Generic brand
Fleece Performance 2019+ 6.7L Coolant Bypass Kit – Modern Fit
Brand: Fleece Performance Engineering
A tailored solution for the newest 6.7L Cummins engines.
For 2019 and newer Ram 2500/3500 trucks with the 6.7L Cummins, this Fleece Performance kit is a direct replacement part. It is made from quality materials and designed to fit your vehicle precisely, ensuring a hassle-free installation. The kit targets the rear cylinder cooling issue that persists in these modern engines.
By improving coolant flow, it helps prevent overheating and pressure buildup, which can lead to head gasket failures. You will appreciate the peace of mind knowing your engine runs cooler under load. If you own a late-model truck, this kit is a smart investment.
- Direct fit for 2019+
- Quality construction
- Prevents overheating
- Only for 2019+ models
- Price not listed
Fleece Performance 07.5-12 6.7L Coolant Bypass Kit – Early 6.7
Brand: Fleece Performance Engineering
A dependable bypass kit for first-generation 6.7L Cummins.
This Fleece Performance kit is made for 2007.5-2012 Dodge/Ram 2500/3500 trucks with the 6.7L Cummins. It is a direct replacement part, so it bolts on without custom fabrication. The quality materials ensure it withstands the heat and pressure of diesel operation.
Designed to fit your vehicle exactly, it addresses the coolant flow issues that cause rear cylinders to run hot. This can prevent cracked heads and blown gaskets, saving you thousands in repairs. If you have an early 6.7L, this kit is a reliable upgrade.
- Exact fit for 07.5-12
- Durable materials
- Prevents rear cylinder damage
- Limited model years
- No extra features listed
Fleece Performance 03-05 5.9L Auto Trans Kit – Leak-Free Design
Brand: Fleece Performance Engineering
A reliable, leak-proof kit for early 5.9L automatic trucks.
This Fleece Performance kit fits 2003-2005 Dodge Ram Cummins 5.9L with automatic transmission. It comes with high-quality AN o-ring fittings and AN hose connections with braided hose, ensuring a leak-free installation. The kit is easy to apply, making it a favorite among DIYers.
As a trusted industry leader, Fleece backs this product with a manufacturer’s warranty. The braided hoses add durability and flexibility, so you can route them cleanly. If you own an early 5.9L auto, this kit is a solid choice to keep your rear cylinders cool.
- Leak-free AN fittings
- Braided hose included
- Manufacturer warranty
- Auto trans only
- Limited to 03-05 models
Bonbo Coolant Bypass Kit – Nylon Braided Hose for 5.9/6.7L
Bonbo’s kit is compatible with 2003-2007 5.9L manual transmission trucks and 2007.5-2018 6.7L models with any transmission. It comes with a nylon braided hose and high-quality AN o-ring fittings, ensuring a leak-free installation. The kit is designed to lower coolant temperature at the rear cylinders, preventing pressure buildup.
This is a must-have for 24-valve engines, as coolant flow to the rear is a known weak point. The complete kit includes everything you need, though professional installation is recommended for best results. If you want a budget-friendly option with broad fitment, this is worth considering.
- Nylon braided hose
- Wide compatibility
- Prevents pressure buildup
- Professional install recommended
- Generic brand
Frailys Coolant Bypass Kit – Reduced Cylinder Head Temp
Brand: Fraylis
A well-built kit that effectively lowers cylinder head temperatures.
Frailys offers precise compatibility with 2003-2007 5.9L manual transmission and 2007.5-2018 6.7L manual or automatic trucks. The kit effectively reduces rear cylinder coolant temperature, preventing harmful pressure buildup under overheating conditions. This helps avoid costly engine damage.
Constructed from high-quality steel and aluminum with a black anodized finish, it resists corrosion. The AN-type O-ring connectors and stainless steel braided hoses provide a leak-proof design. If you want a reliable kit that prioritizes temperature reduction, this is a strong option.
- Reduces rear cylinder temp
- Leak-proof AN connectors
- Corrosion-resistant finish
- Newer brand
- Limited availability
Fleece Performance 98.5-02 5.9L VP Kit – Classic Fit
Brand: Fleece Performance Engineering
A dependable kit for early 24-valve Cummins trucks.
This Fleece Performance kit is compatible with 1998.5-2002 Dodge Ram 5.9 Cummins diesel engines, covering the VP injection era. It includes high-quality AN o-ring fittings and AN hose connections with braided hose, ensuring a leak-free installation. The kit is easy to apply, even for those with basic mechanical skills.
Fleece is a trusted industry leader, and this product is backed by a manufacturer’s warranty. It addresses the rear cylinder cooling issue that affects these older engines, helping you maintain reliability. If you own a classic 24-valve, this kit is a proven upgrade.
- Leak-free fittings
- Braided hose
- Trusted brand
- Only for VP engines
- No color options
Generic Coolant Bypass Kit – Anodized Steel for 5.9/6.7L
Brand: Generic
A cost-effective kit that covers the basics for most Cummins trucks.
This generic kit is compatible with 2003-2007 5.9L manual transmission and 2007.5-2018 6.7L manual or automatic trucks. It lowers coolant temperature at the rear cylinders, ensures consistent temperatures across all cylinders, and prevents damaging pressure buildup. The kit is made from premium aluminum and solid steel with a black anodized surface for durability.
It comes with high-quality AN o-ring fittings for a secure connection. The anodized finish enhances corrosion and oxidation resistance, so it lasts longer. If you are looking for an affordable, no-frills option, this kit delivers the essential benefits.
- Anodized finish
- Consistent temps
- Prevents pressure buildup
- Generic brand
- No warranty mentioned
Fleece Performance 12V Coolant Bypass Kit – 94-98 Stainless
Brand: Fleece Performance Engineering
A robust bypass kit for classic 12V Cummins trucks.
This Fleece Performance kit is designed for 1994-1998 12V Cummins engines, featuring a stainless steel braided line for durability. It is a replacement part made from quality materials, designed to fit your vehicle. The kit addresses the rear cylinder cooling issue that affects these older engines.
With a focus on quality, this kit ensures a reliable seal and long service life. The stainless braided line resists abrasion and corrosion, making it ideal for harsh conditions. If you own a 12V, this kit is a worthy upgrade to protect your engine.
- Stainless braided line
- Quality materials
- Vehicle-specific fit
- Limited to 12V engines
- Price not listed
Buyer’s Guide: What to Consider
Choosing the right coolant bypass kit involves understanding your engine’s needs and the kit’s specifications. Focus on fitment, materials, and ease of installation to ensure you get the best protection for your Cummins.
- Engine Compatibility: Check your engine type (5.9L or 6.7L) and model year. Some kits only fit manual transmissions, while others cover both. Ensure the kit matches your truck to avoid installation issues.
- Material Quality: Look for kits made from aluminum or steel with anodized finishes for corrosion resistance. Braided hoses, whether nylon or stainless steel, offer better durability and leak resistance than rubber.
- Fitting Type: AN o-ring fittings provide a secure, leak-free connection. They are easier to install and maintain compared to barbed fittings. Verify the kit includes all necessary fittings for your application.
- Installation Ease: Consider whether you will install the kit yourself or hire a professional. Kits with direct replacement parts and clear instructions are simpler. Some require more expertise, especially if modifications are needed.
- Brand Reputation: Trusted brands like Fleece Performance offer warranties and proven reliability. Generic options may be cheaper but lack support. Weigh the cost against the peace of mind a reputable brand provides.
Conclusion
Coolant bypass kits are essential for preventing rear cylinder overheating in Cummins engines. Whether you have a 5.9L or 6.7L, there is a kit that fits your truck and budget. Fleece Performance offers reliable, vehicle-specific options, while generic kits provide affordable alternatives.
For most owners, choosing a kit with quality materials and a leak-proof design is key. Consider your model year and transmission type, then pick a kit that meets your needs. Protect your engine and enjoy peace of mind on every drive.
Erica Steven is the founder and lead writer of WorstBrands, a site dedicated to providing honest and trustworthy reviews about outdoor gear and fashion products.
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