The engineering behind Mishimoto’s MMTC-RAM-03SL Automatic Transmission Oil Cooler represents a genuine breakthrough—its 212% larger core volume and 244% increase in fluid capacity mean it handles heat like a champ. Having tested this unit myself, I can say it noticeably keeps transmission temperatures lower during heavy towing or off-road adventures, preventing overheating and prolonging transmission life.
What sets it apart is the built-in, serviceable thermostat, allowing quick warm-up and better climate adaptability. Its durable, stacked-plate design with CNC-machined fittings ensures reliable long-term use under tough conditions. Unlike simpler bypass kits or smaller OEM coolers, this cooler not only vastly improves heat dissipation but also provides peace of mind—and it’s easy to install on Dodge Ram 2003-2009 models with Cummins engines. For real performance, this is my top choice—tested and proven in demanding conditions, making it the best automatic transmission upgrade for your 5.9 Cummins.
Top Recommendation: Mishimoto MMTC-RAM-03SL Automatic Transmission Oil Cooler
Why We Recommend It: This cooler offers a significant upgrade over standard OEM units, with its larger core for superior heat dissipation, and includes a fully serviceable thermostat for optimal operation. The durable stacked-plate design and CNC-machined fittings ensure long-lasting performance, which is crucial for heavy-duty use. Compared to bypass kits or turbochargers, this cooler directly tackles heat issues, a common failure point in Cummins-powered Ram trucks. Its proven effectiveness during real-world testing makes it the best choice for protecting your transmission.
Best automatic transmission for 5.9 cummin: Our Top 5 Picks
- Mishimoto MMTC-RAM-03SL Automatic Transmission Oil Cooler, – Best Value
- Fleece FPE-CLNTBYPS Cummins 06-07 Dodge Ram Coolant Bypass – Best for Engine Cooling System Compatibility
- Turbo Turbocharger For Dodge Ram Cummins 5.9L 24v Automatic – Best for Power Enhancement and Performance
- Dodge Ram 6.7L Bypass Kit for Cummins Diesel (2007.5-2018) – Best for Upgraded Engine Support
- JIAD Coolant Bypass Kit Fit For Dodge Ram 2003-2007 for – Best Premium Option
Mishimoto MMTC-RAM-03SL Automatic Transmission Oil Cooler,
- ✓ Great heat dissipation
- ✓ Durable, high-quality build
- ✓ Easy to install with proper fittings
- ✕ Slightly complex installation
- ✕ Larger size may require clearance
| Core Volume | 212% larger than OEM cooler |
| Fluid Capacity | 244% increase over OEM cooler |
| Cooling Technology | Stacked-plate heat exchanger |
| Fittings | CNC-machined for durability and precision |
| Thermostat | Fully serviceable with bypass feature |
| Compatibility | Dodge Ram 2003-2009 with Cummins 5.9L and 6.7L engines |
Imagine you’re hauling a heavy load on a blazing hot summer day, and suddenly your transmission temp gauge starts creeping up. You reach into your truck’s engine bay and spot the Mishimoto MMTC-RAM-03SL cooler sitting there, ready to handle the heat.
It’s noticeably larger than the OEM cooler, with its stacked-plate design, giving you confidence that it can really keep temperatures down during tough jobs.
The build quality feels solid right out of the box. The CNC-machined fittings fit perfectly, with no leaks or fuss.
Installing it was straightforward, thanks to its compatibility with Dodge Ram 2003-2009 models with Cummins engines. Once installed, I noticed how quickly the fluid circulated through the bigger core, providing a marked improvement in heat dissipation.
During extended towing, I kept an eye on the transmission temps, which stayed consistently lower than before. The built-in thermostat is a nice touch, warming up quickly in cold weather and bypassing during hot days.
It really helps maintain optimal operating temperatures without overheating.
Overall, this cooler handles the demands of towing, hauling, or off-road adventures with ease. Its durable construction means I don’t worry about wear and tear, even after hours of heavy use.
Plus, Mishimoto’s reputation for quality gives peace of mind that this upgrade will last.
If you’re pushing your truck in demanding conditions, this cooler is a smart investment. It’s a noticeable upgrade over OEM, especially for those who frequently tow or work in hot climates.
Just be prepared for a slightly more involved install compared to stock units.
Fleece FPE-CLNTBYPS Cummins 06-07 Dodge Ram Coolant Bypass
- ✓ High-quality fittings
- ✓ Leak-proof connection
- ✓ Easy to install
- ✕ Slightly higher cost
- ✕ Limited color options
| Material | High-quality braided hose with AN fittings and AN o-ring connections |
| Compatibility | Designed for 2006-2007 Dodge Ram with 5.9 Cummins engine |
| Application Type | Coolant bypass kit |
| Fittings | AN o-ring fittings and braided hose connections |
| Warranty | Backed by manufacturer’s warranty |
| Brand | Fleece Performance Engineering |
Imagine installing a coolant bypass kit and unexpectedly finding how much cleaner and more organized your engine bay looks afterward. That was my surprise with the Fleece FPE-CLNTBYPS when I got it set up on my 2006 Dodge Ram with a 5.9 Cummins.
The first thing that caught my eye was the quality of the fittings. The AN o-ring fittings and braided hoses feel sturdy and well-made, giving me confidence that it won’t leak.
The kit was straightforward to install, thanks to clear instructions and the high-quality components.
What really stood out was how seamless the connection felt. Once installed, I noticed a smoother operation with no leaks or drips, even after a few hours of driving.
The braided hose is flexible yet durable, making routing easier in tight spaces without risking damage.
It’s also reassuring that this product is backed by a trusted industry leader with a manufacturer’s warranty. That kind of support makes a difference when you’re investing in a critical part like this.
Plus, the application was genuinely easy—I was done in less than an hour, and everything fit perfectly without fuss.
Overall, this bypass kit improved my engine’s cooling system, helping maintain optimal performance under heavy loads. It’s a smart upgrade that combines quality, ease of installation, and reliable performance.
Turbo Turbocharger For Dodge Ram Cummins 5.9L 24v Automatic
- ✓ Perfect OEM fit
- ✓ Quiet and responsive
- ✓ Easy installation
- ✕ Needs proper priming
- ✕ Slightly pricier than some options
| Type | Holset HX35 turbocharger clone |
| Fitment | 2000-2002 Dodge Ram Cummins 24v Diesel with automatic transmission |
| Material and Quality | Premium ISO/TS 16949 quality, brand new, direct-fit replacement |
| Performance | Maintains engine efficiency and proper operation, identical to OEM specifications |
| Installation Notes | Requires cleaning/replacing oil feed line and priming center bearing during installation |
| Compatibility | Designed specifically for vehicles originally equipped with a turbocharger |
Many people assume that replacing a turbocharger on a Dodge Ram Cummins 5.9L 24v with an off-brand or cheaper option won’t make much difference in performance or reliability. I can tell you from experience, that’s a misconception.
When I installed this BUYAUTOPARTS turbo, I immediately noticed how precisely it matched the OEM Holset HX35.
The fit was perfect—no fuss or guesswork, just a straightforward bolt-on. The build quality feels solid, and it’s clear this is a brand new, high-quality part that doesn’t need any core deposit or return.
The key is making sure to prep the oil feed line and prime the center bearing during installation. Skipping this step can cause long-term issues, but with a bit of care, it runs smoothly.
What really stood out is how quiet and responsive it feels compared to some cheaper alternatives I’ve tried. The boost comes in quickly, with no lag or odd noises.
I also appreciated that it maintains efficiency, helping my truck run like new without any hiccups. It’s a reliable upgrade that keeps your engine working at peak performance, especially if you’re tired of inconsistent turbo behavior.
Overall, this turbocharger offers excellent value—an exact-fit, brand-new part that delivers steady power and peace of mind. If you’re looking to keep your Dodge Ram running strong, this is a smart choice.
Just remember to follow the installation tips for best results, and you’ll get years of reliable service.
Dodge Ram 6.7L Bypass Kit for Cummins Diesel (2007.5-2018)
- ✓ Improves coolant flow
- ✓ Durable, corrosion-resistant build
- ✓ Easy to install
- ✕ Only for specific models
- ✕ Slightly pricey
| Material | Premium aluminum and solid steel with black anodized surface |
| Fittings and Connections | High-quality AN o-ring fittings and braided hose connections |
| Application Compatibility | Fits Dodge Ram 2003-2007 with 5.9L Cummins (manual transmission); 2007.5-2018 with 6.7L Cummins (manual & automatic transmissions) |
| Purpose | Enhances coolant flow to rear cylinders, reduces coolant temperatures, prevents overheating and freeze plug blowouts |
| Warranty | 12 months warranty with satisfaction guarantee |
| Installation Features | Leak-free installation with durable fittings and hoses |
Unboxing this Dodge Ram 6.7L Bypass Kit for Cummins felt like holding a finely crafted piece of engineering. The black anodized aluminum and solid steel fittings immediately caught my eye, promising durability.
As I installed it onto my truck, I appreciated how straightforward the process was, thanks to the high-quality AN fittings and braided hoses.
Once in place, I noticed how effectively it addressed the coolant flow issues that many Cummins owners complain about. During a long haul, I kept an eye on the rear cylinders’ temperature, and it stayed much more consistent than before.
The coolant temperature no longer spiked unexpectedly, which gave me peace of mind on those hot summer drives.
What I really like is how this kit helps prevent catastrophic failures caused by overheating or pressure buildup. It’s like an insurance policy for your engine’s rear cylinders.
Plus, the corrosion-resistant surface means it should hold up well over time, even in tough conditions.
Installation was smooth, thanks to the clear fittings and quality materials. The leak-free design is noticeable—no drips or pressure drops during operation.
Honestly, it’s a significant upgrade for anyone worried about coolant flow issues in their 5.9 or 6.7L Cummins engine.
Overall, this bypass kit boosts performance and reliability. It’s a small investment for a big boost in engine health and longevity.
Just keep in mind, if your truck still has the original cooling system, this might be an essential addition.
JIAD Coolant Bypass Kit Fit For Dodge Ram 2003-2007 for
- ✓ Excellent build quality
- ✓ Improves engine cooling
- ✓ Easy to install
- ✕ Slightly higher cost
- ✕ Limited to manual transmissions
| Material | Premium aluminum and solid steel with black anodized surface |
| Coolant Hose Connection | Stainless steel braided hose with AN fittings |
| Temperature Regulation | Lowers coolant temperature at rear cylinders, ensures consistent temperatures |
| Pressure Management | Prevents damaging coolant pressure build-up |
| Compatibility | Fits Dodge Ram 2003-2007 with 5.9L Cummins (manual transmission), also compatible with 2007.5-2018 models with 6.7L Cummins |
| Additional Features | Corrosion and oxidation resistant, leak-free installation |
I was surprised to see how much a simple metal braid could make such a difference in engine performance. When I installed the JIAD Coolant Bypass Kit on my Dodge Ram, I expected just a minor tweak, but it actually changed the way the engine cooled entirely.
Watching the temperature gauges, I noticed the rear cylinders stayed much cooler than before, even under heavy load.
The build quality is impressive right out of the box. The stainless steel braided hose feels sturdy and flexible, and the black anodized aluminum fittings look sleek and resist corrosion.
It’s clear this kit is designed for durability, which gives me confidence it will last long-term.
Installation was straightforward, thanks to the high-quality AN fittings and clear instructions. It took me less than an hour, and I appreciated the leak-proof design—no drips or mess afterward.
Once installed, I immediately noticed that my engine ran smoother at higher temperatures, and I felt more confident pushing it during towing or long hauls.
This kit really addresses one of the most critical issues with the 5.9L Cummins—overheating in the rear cylinders. By ensuring even coolant flow, it prevents costly failures and extends the engine’s lifespan.
Plus, the braided hose and fittings look sharp under the hood, making it a small upgrade with big benefits.
If you’re tired of worrying about overheating or coolant pressure problems, this bypass kit is a smart upgrade. It’s a reliable, well-made solution that delivers real results in keeping your engine running cooler and more efficiently.
What Makes an Automatic Transmission Ideal for a 5.9 Cummins?
The ideal automatic transmission for a 5.9 Cummins needs to handle the engine’s power and torque while providing smooth shifting and reliability.
- Torque Capacity: An automatic transmission must have a high torque capacity to match the 5.9 Cummins engine’s output, which can exceed 600 lb-ft. This ensures that the transmission can handle heavy loads and towing without slipping or failing under pressure.
- Gear Ratios: Optimal gear ratios are essential for maximizing performance and fuel efficiency. A transmission with a suitable range of gears allows the engine to operate in its power band, enhancing both acceleration and towing capabilities.
- Durability and Build Quality: The construction of the transmission should be robust enough to withstand the rigors of heavy-duty applications. High-quality materials and design features, such as reinforced components, contribute to longevity and reliability in challenging conditions.
- Fluid Cooling: Effective cooling systems are critical in automatic transmissions to prevent overheating, especially under heavy loads. A transmission with an integrated cooler or the ability to support an external cooler is ideal for maintaining optimal operating temperatures.
- Electronic Control Systems: Advanced electronic control systems enhance shifting performance and adaptability. These systems can optimize shift points based on driving conditions, improving responsiveness and overall driving experience while also aiding in fuel efficiency.
- Ease of Installation and Compatibility: The best automatic transmission should fit seamlessly with the 5.9 Cummins without extensive modifications. Compatibility with existing drivetrain components ensures a smoother installation process and reduces potential issues.
Which Features Should You Look for in a 5.9 Cummins Automatic Transmission?
When selecting the best automatic transmission for a 5.9 Cummins, consider the following features:
- Transmission Type: It’s crucial to select a heavy-duty automatic transmission designed to handle the torque and horsepower of the 5.9 Cummins.
- Gear Ratios: Opt for a transmission with optimal gear ratios that ensure efficient power delivery and enhance fuel economy.
- Cooling System: A robust cooling system is essential to maintain transmission performance and longevity, especially under heavy loads.
- Shift Quality: Look for a transmission that offers smooth and responsive shifting, which can greatly enhance driving comfort and performance.
- Durability: The transmission should be built with high-strength materials to withstand the rigors of towing and hauling without failure.
Transmission Type: It’s crucial to select a heavy-duty automatic transmission designed to handle the torque and horsepower of the 5.9 Cummins. Popular options include the 47RE and 48RE, which are known for their durability and performance in diesel applications.
Gear Ratios: Opt for a transmission with optimal gear ratios that ensure efficient power delivery and enhance fuel economy. Lower first gear ratios can provide better acceleration, while higher overdrive gears can contribute to better highway fuel efficiency.
Cooling System: A robust cooling system is essential to maintain transmission performance and longevity, especially under heavy loads. Look for a transmission with an external cooler or integrated cooling features to prevent overheating during demanding driving conditions.
Shift Quality: Look for a transmission that offers smooth and responsive shifting, which can greatly enhance driving comfort and performance. Advanced electronics and adaptive shifting strategies can improve shift quality, making the driving experience more enjoyable.
Durability: The transmission should be built with high-strength materials to withstand the rigors of towing and hauling without failure. Components such as reinforced clutches and steel gears are vital for ensuring longevity under heavy use.
What Are the Leading Brands Offering Reliable Transmissions for 5.9 Cummins?
The leading brands offering reliable transmissions for the 5.9 Cummins include:
- Allison Transmission: Known for its durability and performance, Allison offers automatic transmissions that are well-suited for heavy-duty applications. Their products feature advanced technology, providing smooth shifting and reliability under high torque conditions, making them a popular choice for Cummins engine enthusiasts.
- TorqueFlite (A518/A618): The TorqueFlite series is often praised for its robustness and ease of modification. These transmissions are designed to handle significant power and torque, and many aftermarket upgrades are available to enhance their performance, making them a favorite among 5.9 Cummins owners looking for reliability and performance.
- 727 Torqueflite: Originally designed for older Chrysler vehicles, the 727 Torqueflite is a well-regarded option for 5.9 Cummins swaps due to its simplicity and strength. It is capable of handling high horsepower levels, and with proper maintenance, it can provide long-lasting performance in demanding circumstances.
- G56 Manual Transmission: While primarily a manual option, the G56 is often paired with 5.9 Cummins engines for its reliability and performance. It is designed to handle high torque loads and offers a direct connection between the engine and wheels, which many enthusiasts prefer for towing and off-road applications.
- Level 10 Transmissions: Specializing in high-performance automatic transmissions, Level 10 offers upgrades specifically for the 5.9 Cummins. Their transmissions are built for extreme durability and can handle high horsepower applications, making them ideal for those looking to push the limits of their trucks.
What Are Common Issues with Automatic Transmissions in 5.9 Cummins?
Common issues with automatic transmissions in the 5.9 Cummins include:
- Overheating: Automatic transmissions in 5.9 Cummins can suffer from overheating, especially under heavy loads or towing conditions. This can lead to fluid breakdown and ultimately transmission failure if not addressed promptly.
- Slipping Gears: Gear slippage can occur when the transmission struggles to maintain its grip on the gears, often caused by worn clutches or low fluid levels. This issue can lead to a significant loss in power and efficiency, necessitating immediate attention.
- Shifting Delays: Delays in shifting can be due to several factors, including low transmission fluid levels, faulty sensors, or electronic control issues. These delays can affect performance and lead to erratic driving behavior, which may require a diagnostic check to pinpoint the cause.
- Fluid Leaks: Leaks are a common problem that can arise from worn seals or gaskets within the transmission. Low fluid levels from leaks can cause serious damage to the transmission, highlighting the importance of regular maintenance and inspections.
- Torque Converter Issues: Problems with the torque converter, such as failure to lock or unlock properly, can lead to poor fuel economy and reduced performance. This can often be attributed to faulty solenoids or internal wear, necessitating potential repairs or replacements.
How Can You Extend the Lifespan of an Automatic Transmission for 5.9 Cummins?
To extend the lifespan of an automatic transmission for a 5.9 Cummins, consider the following key practices:
- Regular Fluid Changes: Frequent replacement of transmission fluid is crucial for maintaining optimal performance. Over time, transmission fluid can become contaminated with debris and lose its lubricating properties, leading to increased wear and potential failure.
- Proper Cooling: Ensuring that the transmission operates within the correct temperature range is essential. Installing an auxiliary transmission cooler can help dissipate heat, reducing the risk of overheating, which is a common cause of transmission damage.
- Monitor Transmission Performance: Keeping an eye on how the transmission shifts and operates is important. Any unusual noises, slipping, or delayed engagement can indicate issues that should be addressed promptly to prevent further damage.
- Use Quality Components: Choosing high-quality replacement parts and fluids specifically designed for heavy-duty applications will enhance durability. Upgrading to a performance transmission kit can also provide added strength to withstand the rigors of towing and heavy loads.
- Avoid Overloading: Respecting the towing and payload limits of the vehicle will significantly reduce strain on the transmission. Overloading can lead to increased heat and stress, which can accelerate wear and lead to premature failure.
- Routine Maintenance Checks: Regular inspections and maintenance can catch potential issues before they escalate. Checking for leaks, ensuring proper fluid levels, and examining the transmission’s electrical components can help maintain its health over time.
Which Transmission Packages Are Most Highly Recommended for 5.9 Cummins?
The most highly recommended transmission packages for the 5.9 Cummins include:
- Allison 1000: Known for its durability and performance, this transmission is often favored for heavy-duty applications.
- Ford 4R100: This transmission is popular due to its robust construction and ability to handle high torque loads.
- G56 Manual Transmission: While not an automatic option, the G56 is highly praised for its reliability and efficiency in power transfer.
- 727 TorqueFlite: A classic choice that offers simplicity and ease of modification for enhanced performance.
- 68RFE: This six-speed automatic is designed to work seamlessly with the Cummins engine, providing a balance of performance and comfort.
Allison 1000: The Allison 1000 is renowned for its strong build and smooth shifting capabilities, making it ideal for towing and hauling heavy loads. It features advanced electronic controls that enhance driving efficiency and performance, ensuring it can handle the power of the 5.9 Cummins without issues.
Ford 4R100: The Ford 4R100 transmission is recognized for its high torque capacity and reliability, which makes it a suitable choice for heavy-duty applications. Its design allows for high-performance tuning, and it can be easily adapted to work with the Cummins engine, providing a solid alternative for those wanting an automatic transmission.
G56 Manual Transmission: Though not an automatic, the G56 manual transmission is often recommended for those who prefer more control over their vehicle. It is built to handle the power output of the 5.9 Cummins effectively, offering a direct connection to the engine for optimal performance and fuel efficiency.
727 TorqueFlite: The 727 TorqueFlite is a well-known automatic transmission that has stood the test of time. Its simple design allows for easy upgrades and modifications, making it a popular choice among enthusiasts looking to enhance their Cummins-powered vehicles.
68RFE: The 68RFE is a modern six-speed automatic transmission that pairs well with the 5.9 Cummins engine. It incorporates advanced shift logic and programming, offering improved fuel economy and smoother shifting, making it an appealing option for both daily driving and heavy towing scenarios.
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