Will a 5.9 Valve Cover Fit a 6.7 Cummins Engine?

The Cummins engine family, known for its legendary durability and torque, is widely used in heavy-duty trucks, agricultural machinery, and industrial applications. One of the most popular variants of this engine family is the 5.9L and 6.7L turbo diesel engines, both of which are often found in Dodge Ram trucks. These engines, while sharing many similarities, have distinct differences, particularly when it comes to components such as valve covers. So, if you’re considering swapping or replacing the valve cover on your 6.7L Cummins with one from a 5.9L engine, the question becomes: will a 5.9 valve cover fit a 6.7 Cummins?

In this blog, we’ll explore the key differences between the 5.9 and 6.7 valve covers, why these differences matter, and whether a 5.9 valve cover can be swapped onto a 6.7 engine.

Key Differences Between the 5.9 and 6.7 Cummins Engines

Before diving into the specifics of valve covers, it’s important to understand the primary differences between the 5.9 and 6.7 Cummins engines. These differences influence various components of the engine, including the valve cover.

1. Displacement and Engine Design:
   • 5.9 Cummins: The 5.9L engine has a displacement of 5.9 liters, which was the standard engine for many Dodge Rams, particularly in the late 1990s and early 2000s.
   • 6.7 Cummins: The 6.7L engine, which replaced the 5.9L in the mid-2000s, has a slightly larger displacement (6.7 liters) and features improvements like a more robust rotating assembly, better fuel injection systems, and a redesigned cylinder head. This was done to meet stricter emissions regulations and to improve power and efficiency.
2. Emissions and Turbocharger Differences:
   • 5.9L Engines: The 5.9 engine, particularly the 5.9 24-valve, has fewer emission-related components and a simpler turbo system.
   • 6.7L Engines: The 6.7L engines are equipped with more advanced emissions control systems, including a Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) system, which can affect the physical layout and component clearances in the engine bay.
3. Cooling and Breathing:
   • 6.7L Engine: The 6.7L engine was designed with additional cooling capacity and improvements to airflow, which has resulted in changes to components such as the intake manifold and valve covers.

These differences play a role in determining the fitment of parts between the two engines.

Valve Cover Design: 5.9L vs 6.7L Cummins

The valve cover’s primary function is to protect the top end of the engine and to house components such as the rocker arms and valves. However, it is also home to various sensors, oil passages, and sometimes even the crankcase ventilation system. The design and layout of these systems can vary significantly between the 5.9 and 6.7 engines.

1. Physical Dimensions:
   • The overall physical dimensions of the valve covers are similar in size, but the 6.7L valve cover is often slightly wider or taller in certain areas due to the additional components required for the more complex engine management and emission systems.
2. Gasket Differences:
   • The gaskets for the valve covers also differ between the 5.9 and 6.7 engines. The 6.7L has a gasket with a more complex design to accommodate the extra sensors and other components, while the 5.9L gasket is typically simpler.
3. Sensor and Component Mounting:
   • One of the most significant differences between the two valve covers is the placement of various sensors. The 6.7 valve cover often features additional ports for sensors related to emissions and engine management (such as the Crankcase Ventilation (CCV) system, oil level sensors, and pressure sensors). These sensors and ports may not be present on the 5.9L valve cover. As a result, the 6.7 valve cover has a more complex layout and might not be directly interchangeable with the 5.9 valve cover.
4. Crankcase Ventilation System:
   • The 6.7L Cummins features an updated crankcase ventilation system that is not found on the 5.9L. This system uses a hose and vent system that connects to the valve cover, which could make a direct swap difficult.

Will a 5.9 Valve Cover Fit on a 6.7 Engine?

Now that we’ve reviewed the differences, let’s answer the central question: Will a 5.9 valve cover fit on a 6.7 Cummins engine?

The short answer is: No, it is not a direct fit. Here’s why:

1. Design Differences: As mentioned earlier, the 6.7L Cummins engine has a different layout, with additional components and sensors that are not present on the 5.9L. These components, such as the venting system, oil pressure sensors, and more complex gasket design, will not line up with the simpler 5.9 valve cover.
2. Sensor Compatibility: The sensor locations and mounting points on the 6.7L valve cover differ from the 5.9L, meaning that if you tried to install a 5.9 valve cover, you would not have the necessary connections for sensors or hoses related to the crankcase ventilation system.
3. Gasket and Seal Issues: Even if you were to attempt the swap, the gasket for the 5.9 valve cover may not provide a proper seal on the 6.7 engine, leading to potential oil leaks.
4. Fitment Issues: While the overall size of the valve covers may appear similar, the additional components (such as the EGR system, the DPF, and the other emission components in the 6.7L engine) create space constraints that prevent a 5.9 valve cover from fitting properly.

Alternatives to Swapping Valve Covers

If you’re looking to replace a valve cover on your 6.7L Cummins, it’s advisable to use the appropriate 6.7L valve cover. There are several aftermarket options available for the 6.7L engine that can improve performance or aesthetics, such as vented valve covers for improved crankcase ventilation, or polished covers for a cleaner look.

Additionally, if you want to modify the engine or improve certain aspects of its performance, you may consider upgrading the components that are compatible with the 6.7 engine rather than attempting to use parts from the 5.9.

Conclusion

While both the 5.9 and 6.7 Cummins engines share a common heritage and many components, their valve covers are not directly interchangeable. The 6.7L engine’s additional components, sensor mounting locations, and the more complex emissions systems create significant differences that make swapping a 5.9 valve cover onto a 6.7 engine impractical and likely ineffective. If you’re in need of a replacement valve cover for your 6.7L engine, it is best to source one specifically designed for that engine.