2018 6.7 Cummins Specs: The Definitive Guide to Power, Towing, and Reliability

The 2018 6.7L Cummins: Pinnacle of a Generation

The 2018 model year holds a special place in the history of the Ram-Cummins partnership. It represents the final, most powerful, and most refined version of the 6.7L Cummins Turbo Diesel within the fourth-generation Ram Heavy Duty platform (2010-2018). This engine is the culmination of nearly a decade of incremental improvements, pushing the boundaries of torque and capability in the consumer truck market.

The 6.7L engine itself was born out of necessity. Its predecessor, the legendary 5.9L Cummins, could no longer be modified to meet increasingly stringent emissions regulations without compromising performance. Introduced in mid-2007, the 6.7L featured a larger bore and a longer stroke, providing a platform that could simultaneously increase power output and accommodate modern emissions control systems like the Diesel Particulate Filter (DPF).

For 2018, the engine’s core identity remained firmly rooted in its workhorse heritage. The inline-six configuration, a Cummins hallmark, provides inherent primary balance for smooth operation and is renowned for producing tremendous low-end torque. This power plant, built with a robust cast-iron block and head, served as the premier engine option for the 2018 Ram 2500, 3500, and commercial Chassis Cab models, solidifying its reputation for strength and durability.

Core Engine Specifications: The Heart of the Beast

Before exploring the different power ratings and applications, it is essential to understand the foundational architecture of the 2018 6.7L Cummins. These core specifications are shared across all versions of the engine, forming the basis for its legendary performance.

Table 1: General 2018 6.7L Cummins Specifications

Key Feature Deep Dive

Several key engineering features define the 6.7L Cummins’s character and capability:

• Cast-Iron Foundation: The engine is built on a deep-skirt cast-iron block featuring Siamese cylinder bores, a design where adjacent cylinder walls are joined without a water jacket between them. This significantly increases block rigidity, allowing it to safely withstand the immense cylinder pressures required to produce over 900 lb-ft of torque.
• Holset VGT Turbo: The Holset HE351VE Variable Geometry Turbocharger is a critical component. By using electronically controlled vanes, it can alter the exhaust housing’s aspect ratio on the fly. At low engine speeds, the vanes constrict to increase exhaust gas velocity, making the turbo spool up quickly for immediate throttle response, much like a small turbo. At higher engine speeds, the vanes open up to maximize exhaust flow for peak horsepower, mimicking a large turbo. This technology is also the key to the engine’s class-exclusive “smart” diesel exhaust brake, which uses the turbo to create backpressure for controlled descents with heavy loads.
• Bosch HPCR Fuel System: The Bosch high-pressure common-rail fuel system is the heart of the engine’s power and efficiency. The Bosch CP3 injection pump pressurizes fuel up to 29,000 PSI into a common “rail” that feeds all six electronic solenoid injectors. This extremely high pressure allows for finer atomization of the diesel fuel, leading to a more complete and powerful combustion event. This precision is vital for maximizing horsepower and torque while controlling emissions.

Power & Performance: A Tale of Three Transmissions

A crucial aspect of the 2018 6.7L Cummins is that its performance specifications are not monolithic. Instead, the engine’s output is deliberately tailored to the specific vehicle application and, most importantly, the transmission it is paired with. This strategy was implemented by Ram to match the engine’s immense torque potential with the mechanical limitations of the gearboxes, ensuring long-term durability across the lineup.

The highest power ratings were reserved exclusively for the transmissions engineered to handle them. As the market trended heavily toward automatic transmissions, Ram paired its highest torque engine variant with the robust Aisin automatic, while de-rating the output for the standard-duty automatic and the rarely-optioned manual transmission. This ensures that each powertrain combination operates within a safe and reliable margin.

Furthermore, a distinction exists between the consumer-focused Ram 2500/3500 pickups and the work-oriented 3500/4500/5500 Chassis Cab models. The Chassis Cabs, designed for constant, grueling commercial use, long idle times, and Power Take-Off (PTO) operation, received a de-tuned version of the engine to prioritize ultimate longevity and reliability over peak performance numbers.

Table: 2018 Cummins Horsepower & Torque by Application & Transmission

Analysis of Each Variant

• The Manual (G56): The Mercedes-sourced G56 6-speed manual transmission was the choice for traditionalists. However, to preserve the gearbox, its torque rating was the lowest of the pickup offerings at 660 lb-ft. By 2018, this option was a rarity, reflecting the industry’s shift away from manual transmissions in heavy-duty trucks.
• The Standard Automatic (68RFE): This Chrysler-built 6-speed automatic was the most common transmission found in Ram 2500 models and standard-output 3500s. It offered a substantial torque increase to 800 lb-ft, making it a far more capable towing machine than its manual counterpart. However, among enthusiasts, the 68RFE is often considered a weak point, particularly if engine power is increased beyond stock levels.
• The High-Output Automatic (Aisin AS69RC): Topping the 2018 lineup was the High-Output engine, available exclusively in the Ram 3500 and paired with the commercial-grade Aisin 6-speed automatic transmission. This combination unleashed the engine’s full potential, delivering a class-leading 930 lb-ft of torque. The heavier-duty Aisin was necessary to reliably handle this monumental output, making this powertrain the undisputed king of the hill for towing and hauling in the 2018 Ram lineup.

2018 Ram Towing & Payload Capacities

The ultimate purpose of the 6.7L Cummins’s massive torque is to move heavy loads. However, the engine’s raw power is only one part of the equation. A truck’s real-world towing and payload capacities are determined by a complex interplay of factors, including its frame, suspension, axles, and configuration. For the 2018 Ram lineup, this means that capability figures vary significantly based on cab type (Regular, Crew, Mega), bed length, drivetrain (4×2 or 4×4), rear axle ratio (e.g., 3.42, 3.73, 4.10), and whether it has single or dual rear wheels (SRW/DRW).

Understanding this variation is critical for any potential buyer. For example, a 2018 Ram 3500 with the Cummins engine could have a maximum towing capacity anywhere between approximately 15,000 pounds and over 31,000 pounds. The key to unlocking the highest towing figures almost always involves selecting a Ram 3500 with a dual-rear-wheel configuration, the High-Output engine/Aisin transmission combination, and the shortest possible axle ratio (4.10). For those looking to maximize their truck’s work potential, understanding the full is essential.

Ram 2500 Towing & Payload Summary

The Ram 2500, equipped exclusively with a single-rear-wheel axle, offers a potent blend of daily drivability and heavy-duty capability.

Table: 2018 Ram 2500 6.7L Cummins Capability Range

Ram 3500 Towing & Payload Summary

The Ram 3500 is where ultimate capability is found, especially in its dual-rear-wheel (dually) configurations, which provide the stability needed for the heaviest loads.

Table 4: 2018 Ram 3500 6.7L Cummins Capability Range

Reliability, Common Problems, and Long-Term Ownership

The 6.7L Cummins engine carries a strong reputation for durability, but like any modern diesel, it has known weaknesses that potential owners should be aware of. The ownership experience often presents a paradox: the core mechanical components of the engine are exceptionally robust, while the complex ancillary systems required for emissions control and performance can be sources of frustration and costly repairs.

The Good: Built to Last

At its core, the 2018 6.7L Cummins is an engine built for longevity. With diligent maintenance, these engines are well-known to surpass 250,000 to 300,000 miles. The foundation of this durability lies in its heavy-duty construction, including the stout cast-iron block and cylinder head and a robust rotating assembly designed from the outset for high-stress, commercial applications.

The Common Issues: What to Watch For

Long-term reliability is often dictated not by the engine block itself, but by the components bolted to it. Most of the common issues reported for the fourth-generation 6.7L Cummins are related to these supporting systems.

• Emissions System Failures: This is the most frequently cited source of problems. The complex emissions system includes an Exhaust Gas Recirculation (EGR) valve, an EGR cooler, and a Diesel Particulate Filter (DPF). The EGR valve can become clogged with soot and stick, the EGR cooler can crack and leak coolant, and the DPF can become clogged, forcing the truck into a power-reducing “limp mode.” These problems are often made worse by frequent short trips, excessive idling, or light-duty use where the exhaust system doesn’t get hot enough to perform its self-cleaning “regeneration” cycles.
• Variable Geometry Turbo (VGT) Failure: The electronic actuator on the Holset VGT is a known weak point. Over time, soot and carbon buildup within the turbo’s housing can cause the delicate internal vanes to stick or seize. This leads to poor performance, check engine lights, loss of the exhaust brake function, and can eventually require a costly replacement of the entire turbocharger assembly.
• Heater Grid Bolt Failure: A well-documented and potentially catastrophic issue involves the bolt that secures the electrical connection to the intake air heater grid. This bolt can loosen over time, break off, and fall directly into the intake manifold, where it is often ingested by the #6 cylinder. This can cause severe damage to the piston, cylinder head, and valves, potentially requiring a complete engine rebuild. Preventative solutions are available in the aftermarket.
• 68RFE Transmission Weaknesses: While not a direct engine failure, the standard-duty 68RFE automatic transmission is often cited as a weak link in the powertrain. It can struggle to handle the Cummins’s massive torque, especially when towing at its limit or if power has been increased with aftermarket tuning. A common failure point is the accumulator plate, which can lead to a costly valve body repair.

Real-World Fuel Economy

Heavy-duty trucks like the Ram 2500 and 3500 are exempt from official EPA fuel economy ratings due to their weight. Therefore, real-world data reported by owners is the best measure of what to expect. Fuel economy is highly variable based on driving style, load, terrain, and vehicle configuration.

• City MPG: 13-16 MPG
• Highway MPG (unloaded): 17-22 MPG. Many owners report a “sweet spot” for efficiency at speeds around 65 mph.
• Towing MPG: 9-13 MPG. This figure is heavily dependent on the weight of the trailer and the terrain.

Recommended Maintenance Schedule

Adhering to a rigorous maintenance schedule is the most effective strategy for mitigating the common problems associated with the 6.7L Cummins and ensuring it reaches its full life expectancy. Following the manufacturer’s recommended service intervals, especially for fuel filters, oil changes, and the crankcase ventilation filter, is critical for long-term health. Learning about proper diesel engine maintenance tips can save owners thousands in potential repair costs.

Table 5: 2018 6.7L Cummins Recommended Maintenance Intervals

Safety & Recalls

The 2018 Ram 2500 and 3500 models have been subject to several important safety recalls issued by the National Highway Traffic Safety Administration (NHTSA). It is imperative for any current or prospective owner to verify that these recalls have been addressed by a certified dealer. A vehicle’s specific recall status can be checked on the(https://www.nhtsa.gov/recalls) using its Vehicle Identification Number (VIN).

The recalls point to specific vulnerabilities in the vehicle’s manufacturing and design. The most critical recalls involve primary vehicle control systems, such as brakes and steering, and represent significant safety risks if left unaddressed. Making recall compliance a non-negotiable part of any pre-purchase inspection is highly recommended.

Key Recalls for the 2018 Model Year

• NHTSA #24V896000: Hydraulic Control Unit (HCU) Failure: This is the most significant recall, affecting over 300,000 vehicles. A defect in the HCU can cause a failure of the anti-lock brake (ABS), electronic stability control (ESC), and traction control systems. This loss of critical safety functions can substantially increase the risk of a crash. The recall was prompted by thousands of consumer complaints.
• NHTSA #19V021000: Steering Linkage Separation: This recall addresses an issue where the jam nut on the steering linkage can loosen, potentially allowing the drag link to separate. A drag link separation would result in a complete and sudden loss of steering control.
• NHTSA #19V347000: Tailgate Latch Failure: On trucks equipped with a power-locking tailgate, a component in the latch mechanism can fracture. This can cause the tailgate to unlatch and open unexpectedly while the vehicle is in motion, creating a road hazard from falling cargo.
• NHTSA #18V332000: Cruise Control Cannot Be Canceled: Affecting nearly 5 million FCA vehicles, this recall was for a software issue that could, under specific circumstances, prevent the driver from deactivating the cruise control, potentially leading to unintended acceleration.

Frequently Asked Questions (FAQs)

What is the horsepower and torque of a 2018 6.7 Cummins?

The output depends entirely on the transmission. The 6-speed manual version produces 350 hp and 660 lb-ft of torque. The standard 6-speed automatic (68RFE) is rated for 370 hp and 800 lb-ft. The High-Output version, exclusive to the Ram 3500 with the Aisin automatic, delivers 385 hp and 930 lb-ft of torque.

How much can a 2018 Ram 2500 with the 6.7 Cummins tow?

When properly configured, a 2018 Ram 2500 with the 6.7L Cummins can tow a maximum of 17,980 pounds.

What is the max towing capacity of a 2018 Ram 3500 Cummins?

The maximum towing capacity for a 2018 Ram 3500 is 31,210 pounds. This requires the High-Output engine, the Aisin transmission, a dual-rear-wheel configuration, and the 4.10 axle ratio.

Is the 2018 6.7 Cummins a reliable engine?

The core mechanical engine is considered very reliable and can last well over 300,000 miles with proper care. However, the overall vehicle’s reliability can be affected by common and expensive issues with its emissions systems (DPF, EGR) and the VGT turbocharger.

What is the real-world MPG for a 2018 6.7 Cummins?

Real-world fuel economy typically ranges from 13-16 MPG in city driving, 17-22 MPG on the highway when unloaded, and 9-13 MPG when towing heavy loads.

What are the most common problems with the 2018 6.7 Cummins?

The most widely reported problems are related to the emissions system, including clogged Diesel Particulate Filters (DPF) and failing Exhaust Gas Recirculation (EGR) components. Other common issues include VGT turbo actuator failure and the potential for the intake heater grid bolt to break and fall into the engine, causing catastrophic damage.