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Understanding the Engine Landscape in Heavy-Duty Trucks
When selecting a powerplant for a new dump truck—especially one paired with an Allison automatic transmission—the choice often narrows to two contenders: the PACCAR MX series and the Cummins ISX lineup. Both engines are widely available in Kenworth and Peterbilt trucks, but they differ significantly in design philosophy, serviceability, and long-term reliability.
PACCAR, which owns Kenworth and Peterbilt, has pushed its proprietary MX engines into its truck lineup, while Cummins remains a trusted third-party supplier with decades of proven performance. The decision between the two isn’t just about horsepower—it’s about maintenance, drivability, and how well the engine integrates with your operation.
Terminology Clarification
- MX13: PACCAR’s flagship 12.9-liter engine, designed in Europe and adapted for North American trucks. Known for its compact packaging and fuel efficiency.
- ISX12/ISX15: Cummins’ heavy-duty inline-six engines, available in multiple displacements and horsepower ratings. Known for robust torque and widespread service support.
- Allison Transmission: A fully automatic transmission commonly used in vocational trucks. Offers smooth shifting and reduced driver fatigue.
- EGR Cooler: Exhaust Gas Recirculation component that reduces NOx emissions but can be prone to clogging and failure.
- Aftertreatment System: Emissions control system including DPF (Diesel Particulate Filter), SCR (Selective Catalytic Reduction), and DEF (Diesel Exhaust Fluid) dosing.
Performance and Drivability
Drivers who have tested both engines report noticeable differences in throttle response and shift behavior:
Cummins engines are widely regarded as easier to work on, with simpler layouts and better access to components. PACCAR MX engines, by contrast, often present a more crowded engine bay with complex wiring and proprietary parts.
Common service observations include:
The PACCAR MX engine is derived from the DAF MX platform used in European trucks. While refined for North American conditions, it lacks the long-term field history of the Cummins ISX, which has evolved from the N14 and ISM platforms over decades.
Interestingly, PACCAR’s PX engines are rebadged Cummins units (such as the 6.7L and 8.9L), but the MX series is entirely PACCAR’s own design. This distinction is critical when evaluating parts compatibility and service networks.
Real-World Case Study: Fleet Comparison
A Canadian fleet operating three trucks—two with Cummins ISX15 engines and one with a PACCAR MX13—reported the following:
The use of “wonder oil” to address oil consumption in ISX engines echoes older practices from the mid-20th century. Mechanics once added Bon Ami abrasive powder to the intake of Caterpillar and other engines to help seat piston rings. While modern oil filtration systems make such practices obsolete, the concept of temporary abrasive additives persists in specialized break-in oils.
Recommendations for Buyers
When choosing between PACCAR MX and Cummins ISX engines, consider the following:
- If serviceability and parts availability are top priorities, Cummins is the safer bet.
- For fleets with in-house PACCAR expertise or access to dealer support, the MX13 may offer fuel savings and integration benefits.
- Always test drive both configurations with your preferred transmission to assess throttle response and shift logic.
- Request reprogramming of transmission shift points if the factory settings feel sluggish, especially with Allison automatics.
- Investigate warranty coverage and service networks in your region before committing.
Suggested Parameters for Evaluation
When comparing engine options, evaluate:
While PACCAR continues to refine its MX engine platform, many operators still favor Cummins for its simplicity, reliability, and extensive support network. In the demanding world of dump trucks and vocational hauling, downtime is costly—and the engine you choose can make or break your bottom line. Whether you’re refurbishing a quad-axle or spec’ing a new build, the decision between PACCAR and Cummins should be grounded in real-world performance, not just dealership inventory.
When selecting a powerplant for a new dump truck—especially one paired with an Allison automatic transmission—the choice often narrows to two contenders: the PACCAR MX series and the Cummins ISX lineup. Both engines are widely available in Kenworth and Peterbilt trucks, but they differ significantly in design philosophy, serviceability, and long-term reliability.
PACCAR, which owns Kenworth and Peterbilt, has pushed its proprietary MX engines into its truck lineup, while Cummins remains a trusted third-party supplier with decades of proven performance. The decision between the two isn’t just about horsepower—it’s about maintenance, drivability, and how well the engine integrates with your operation.
Terminology Clarification
- MX13: PACCAR’s flagship 12.9-liter engine, designed in Europe and adapted for North American trucks. Known for its compact packaging and fuel efficiency.
- ISX12/ISX15: Cummins’ heavy-duty inline-six engines, available in multiple displacements and horsepower ratings. Known for robust torque and widespread service support.
- Allison Transmission: A fully automatic transmission commonly used in vocational trucks. Offers smooth shifting and reduced driver fatigue.
- EGR Cooler: Exhaust Gas Recirculation component that reduces NOx emissions but can be prone to clogging and failure.
- Aftertreatment System: Emissions control system including DPF (Diesel Particulate Filter), SCR (Selective Catalytic Reduction), and DEF (Diesel Exhaust Fluid) dosing.
Performance and Drivability
Drivers who have tested both engines report noticeable differences in throttle response and shift behavior:
- The MX13 paired with an Allison transmission tends to shift at higher RPMs (around 1700), which can feel sluggish unless reprogrammed.
- The ISX12 with an 8LL manual or automated transmission delivers more immediate torque and a familiar feel reminiscent of older mechanical engines.
- Jake brake performance is strong on both, but Cummins systems tend to be more consistent across models.
Cummins engines are widely regarded as easier to work on, with simpler layouts and better access to components. PACCAR MX engines, by contrast, often present a more crowded engine bay with complex wiring and proprietary parts.
Common service observations include:
- PACCAR MX engines frequently trigger engine lights due to minor electrical faults, requiring frequent shop visits.
- Cummins ISX engines have experienced oil consumption issues in some units, addressed by a temporary use of a specialized “wonder oil” formulated to seat rings and reduce blow-by.
- Cummins service intervals and costs are generally lower, with more independent shops equipped to handle repairs.
The PACCAR MX engine is derived from the DAF MX platform used in European trucks. While refined for North American conditions, it lacks the long-term field history of the Cummins ISX, which has evolved from the N14 and ISM platforms over decades.
Interestingly, PACCAR’s PX engines are rebadged Cummins units (such as the 6.7L and 8.9L), but the MX series is entirely PACCAR’s own design. This distinction is critical when evaluating parts compatibility and service networks.
Real-World Case Study: Fleet Comparison
A Canadian fleet operating three trucks—two with Cummins ISX15 engines and one with a PACCAR MX13—reported the following:
- The MX13 truck had consistent electrical issues and higher service costs.
- The ISX15 trucks, despite one requiring an EGR cooler replacement and another burning oil, were more reliable overall.
- Fuel economy was slightly better on the Cummins units, and downtime was significantly lower.
The use of “wonder oil” to address oil consumption in ISX engines echoes older practices from the mid-20th century. Mechanics once added Bon Ami abrasive powder to the intake of Caterpillar and other engines to help seat piston rings. While modern oil filtration systems make such practices obsolete, the concept of temporary abrasive additives persists in specialized break-in oils.
Recommendations for Buyers
When choosing between PACCAR MX and Cummins ISX engines, consider the following:
- If serviceability and parts availability are top priorities, Cummins is the safer bet.
- For fleets with in-house PACCAR expertise or access to dealer support, the MX13 may offer fuel savings and integration benefits.
- Always test drive both configurations with your preferred transmission to assess throttle response and shift logic.
- Request reprogramming of transmission shift points if the factory settings feel sluggish, especially with Allison automatics.
- Investigate warranty coverage and service networks in your region before committing.
Suggested Parameters for Evaluation
When comparing engine options, evaluate:
- Horsepower range: MX13 (405–510 hp), ISX12 (350–450 hp), ISX15 (400–600 hp)
- Torque output: MX13 (1,450–1,850 lb-ft), ISX15 (1,450–2,050 lb-ft)
- Oil change intervals: MX13 (up to 60,000 miles), ISX (typically 25,000–50,000 miles depending on duty cycle)
- Emissions system complexity: MX13 uses integrated SCR and DPF; ISX uses modular aftertreatment components
While PACCAR continues to refine its MX engine platform, many operators still favor Cummins for its simplicity, reliability, and extensive support network. In the demanding world of dump trucks and vocational hauling, downtime is costly—and the engine you choose can make or break your bottom line. Whether you’re refurbishing a quad-axle or spec’ing a new build, the decision between PACCAR and Cummins should be grounded in real-world performance, not just dealership inventory.
