Replacing a QSK19 with a Mitsubishi S6R-Y3 and S6R2-Y3

Replacing a QSK 19 with a Mitsubishi S6R and S6R2

This comparison evaluates the Cummins QSK19 and Mitsubishi S6R platforms using continuous-duty ratings intended for unlimited-hour operation. The 660 HP QSK19 aligns most directly with the S6R-Y3 (684 HP @ 1800 RPM) as a practical repower option, while the 750 HP QSK19 can be addressed with the S6R2-Y3 (803 HP @ 1400 RPM) but requires a more invasive and higher-cost conversion. Continuous-duty ratings provide the most accurate framework for evaluating repower feasibility and long-term operating impact.

Jump to: 

• Comparison to the S6R-Y3
• Comparison to the S6R2-Y3
• Brief Background: Cummins QSK Series
• Common Modifications to Plan For
• Third Party Stories
• Target Markets
• QSK19 Operators IRR as of March 2022
• Sales Strategy
• Repower Planning Summary

Comparison to the S6R-Y3

Attribute	QSK 19	Mitsubishi S6R-Y3
Tier	2	3
Power	660 HP @ 1800 RPM	684 HP @ 1800RPM
Configuration	Inline-6 , 4-Stroke	Inline-6, 4-Stroke
Displacement	19 L	24.51 L
JW (BTU/min)	25,400	N/A
AC (BTU/min)	N/A	N/A
Fuel Burn (GPH)	33.6	N/A

 

Comparison to the S6R2-Y3

Attribute	QSK 19	Mitsubishi S6R2-Y3
Tier	3	3
Power	750 HP @ 1800 RPM	803 HP @ 1400RPM
Configuration	Inline-6 , 4-Stroke	Inline-6, 4-Stroke
Displacement	19 L	29.96 L
JW (BTU/min)	20400	N/A
AC (BTU/min)	6099	N/A
Fuel Burn (GPH)	37.2	N/A

Dimension Delta Comparisons:

Dimension	QSK19 Base (in)	Δ S6R-Y3 (in)	Δ S6R2-Y3 (in)
Length	79.00	–8.00	–8.96
Width	38.00	+6.00	+5.03
Height	74.00	–10.00	–7.29

Brief Background: Cummins QSK Series

• Cummins KTA series engines were fully mechanical and long used in workboat and inland markets.

• The QSK series replaced the KTA line, introducing electronically controlled engines beginning in 2005.

• This transition marked Cummins’ shift from mechanical systems to electronic engine management.

• Some operators prefer mechanical engines for their simplicity, which has influenced repower decisions over time. 

Common Modifications to Plan For

Cooling System

QSK19 660HP → S6R-Y3 (684 HP @ 1800 RPM)

• Early QSK19 Tier 2 engines are dual-circuit, but many vessels use one large grid cooler to serve both jacket water and aftercooler.

• The S6R requires separate cooling circuits for jacket water and aftercooler.

• In documented repowers:

  • Existing grid cooler was sufficient for the aftercooler circuit.

  • A new jacket water grid cooler was added to meet S6R requirements.

• Adding a jacket water cooler is generally less expensive and easier to package than upsizing an aftercooler.

QSK19 750HP → S6R2-Y3 (803 HP @ 1400 RPM)

• Vessels typically already have two grid coolers, but additional cooling capacity is still required.

• Grid coolers often need to increase in size to handle higher heat rejection.

• Cooling system changes are more extensive than the 660 HP repower.

Exhaust System

Applies to both S6R and S6R2

• Mitsubishi engines require a 10-inch muffler.

• Many QSK19 installations use 8-inch mufflers.

• Exhaust piping may remain unchanged, but:

  • Muffler diameter must increase

  • Adequate space in the exhaust stack should be verified during survey.

Piping & Systems

Applies to both S6R and S6R2

• Coolant piping rerouting is required due to different cooling circuit layouts.

• General system reconfiguration is expected when installing a new engine platform.

Drivetrain & Propulsion

QSK19 660 → S6R-Y3

• S6R produces slightly more horsepower than the 660 HP QSK19.

• Propeller modifications may be required to absorb the additional power.

• Gear changes are typically not required due to matching 1800 RPM ratings.

QSK19 750 → S6R2-Y3

• S6R2 operates at 1400 RPM, creating a major RPM mismatch.

• Gear change is almost always required, as gearbox horsepower ratings decrease at lower RPM.

• New gear ratio and propeller changes are required.

• This significantly increases cost and installation complexity.

Displacement & Engine Architecture Note

Across comparable horsepower classes, Mitsubishi R-Series engines carry significantly greater displacement than their Cummins QSK counterparts. On average, the R-Series platforms are approximately 24% larger in displacement at similar horsepower ratings. For example, the QSK19 (19 liters) aligns with the Mitsubishi S6R at 25 liters, the QSK38 (38 liters) aligns with the S12R at 49 liters, and the QSK50 aligns with the S16R at 65 liters. This increase in displacement reflects larger internal components and heavier rotating assemblies, which is a key factor when evaluating physical size, structural loading, and long-term durability at continuous duty ratings.

Third Party Stories

M/V Jack Haskel – QSK19 (660 HP) to S6R-Y3 Repower

March 2022

• In March 2022, the M/V Jack Haskel  initiated plans to repower a pair of Tier 2 Cummins QSK19 (660 HP) engines with Mitsubishi S6R-Y3 (684HP) engines.

• The existing QSK19 engines had approximately 25,000 operating hours and were considered end-of-life by the operator.

• Primary drivers for the repower included:

  • Ongoing reliability issues

  • Parts availability challenges, including vessel downtime while waiting on components

  • Inability to achieve the desired service life from the QSK19 platform

• The vessel was originally equipped with one large grid cooler serving both jacket water and aftercooler circuits on the QSK19 engines.

• As part of the repower planning:

  • The existing grid cooler was determined to be adequate for the aftercooler circuit on the S6R

  • A new jacket water grid cooler was purchased for installation

• At the time of this review, the repower had not yet been completed, though engines had been purchased and installation was planned for a later date.

L&L Marine – New Construction Transition from Cummins to Mitsubishi

• L&L Marine was historically a Cummins-loyal fleet, with extensive experience on both KTA and QSK platforms.

• While the operator had strong success with KTA engines, they consistently saw limited service life (20,000–25,000 hours) from QSK engines and were unable to extend that lifespan.

• The decision to move away from QSK engines was driven by a desire for greater engine life and durability, not brand preference.

• A key turning point was reviewing:

  • Physical size

  • Displacement

  • Internal component robustness, including connecting rod size

• The operator ultimately selected Mitsubishi R-series engines (including S6R2) for new construction.

• Since making the transition, the operator has:

  • Reported positive performance and durability feedback

  • Actively recommended Mitsubishi engines to other operators seeking referrals

Target Markets

• Push Boats
• Tug Boats
• Crew Boats

QSK 19 Operators IRR as of March 2022

Operator	Qty
Kirby Inland Marine LP	22
Blessy Marine Services, Inc.	18
Enterprise Marine Services LLC	17
Devall Towing & Boat Service	14
American River Transportation Co. LLC	11
Gnotts Reserve, Inc.	11
American Commercial Barge Line LLC	10
Illinois Marine Towing, Inc.	8
Gateway Dredging & Contracting LLC	6
SCF Waxler Marine LLC	6
C&B Marine LLC	6
Garber Bros., Inc.	4
McGinnis, Inc.	4
Superior Marine, Inc.	4
Carline Companies	4
Buffalo Marine Service, Inc.	4

Sales Strategy

Sales Strategy Consideration: 750 HP QSK19 on New Builds

• Vessels originally built with the 750 HP QSK19 become difficult and expensive repower candidates later.

• The primary drivers are the RPM difference and resulting impacts to gearing, propellers, and cooling systems.

• Because of this, it is critical to position Mitsubishi early on new builds, rather than relying on future repower opportunities once a 750 HP QSK19 is installed.

Core Pain Point: Engine Life

• The primary pain point with Cummins QSK engines is engine life, especially on the QSK19 and QSK38.

• Operators commonly report 25,000–30,000 hours before replacement.

• In some cases, Cummins has stated directly that engines should be expected to be replaced around 25,000 hours, including references to QSK and KTA 50 platforms.

• Customers consistently express dissatisfaction with this lifecycle for continuous-duty operations.

Failure Type Observed

• Failures are often major bottom-end failures, not just top-end wear.

• Reported failure areas include:

  • Crankshafts

  • Main bearings

  • Connecting rod and rod bearings

• These failures tend to occur earlier than expected and often require full engine replacement.

Parts Availability & Support

• Parts availability is a frequent and ongoing complaint with Cummins.

• Customers report vessels being tied up waiting on parts, sometimes for months.

• Many operators feel Cummins customer service has declined significantly compared to past experience.

• Customers are often told supply chain issues may take 12–18 months to resolve.

Sales Approach: Let the Customer Talk

• Most customers are already experiencing pain and do not need to be convinced.

• Simply asking about:

  • Engine life

  • Parts availability

  • Downtime experience
    often leads customers to openly share frustration.

• Allowing customers to talk through their own experience naturally surfaces the issues.

Mitsubishi Positioning 

• Mitsubishi engines are positioned as:

  • Longer-life assets

  • Lower lifecycle cost based on observed service history

• Typical Mitsubishi experience discussed includes:

  • Top-end work at 20,000–25,000 hours

  • Engines operating 60,000–100,000 hours without bottom-end work

• Support is framed around:

  • Strong parts availability

  • Faster engine delivery timelines

  • Ongoing customer support

Objections: Modifications & Cost

• Required repower modifications can appear costly and become an objection.

• Examples discussed include:

  • Gear ratio changes

  • Grid cooler additions or upsizing

• The strategy is to compare one-time modification cost against:

  • Ongoing downtime

  • Repeated failures

  • Lost revenue from vessels being down

• Modifications are a one-time event, while engine-related pain is recurring.

Electronics & Control Dependency

• QSK engines are fully electronic, placing operators at the mercy of Cummins for:

  • Diagnostics

  • Service access

  • Resolution timelines

• Mitsubishi is positioned around:

  • Empowering customers and local service

  • Reducing dependency on factory service response by allowing work on your own vessel

Repower Planning Summary

Primary Changes:

QSK19 (660 HP) → S6R-Y3 (684 HP @ 1800 RPM)

• Addition of a separate jacket water cooling circuit

• Installation of a new jacket water grid cooler (existing cooler often reused for aftercooler)

• Coolant piping rerouted to accommodate separate cooling circuits

• Muffler upsized to 10-inch (exhaust piping may remain)

• Propeller modifications to absorb slightly higher horsepower

QSK19 (750 HP) → S6R2-Y3 (803 HP @ 1400 RPM)

• Gear change required due to lower operating RPM

• New gear ratio and drivetrain reconfiguration

• Propeller replacement or significant modification

• Increased cooling capacity, including larger grid coolers

• Coolant piping rerouted

• Muffler upsized to 10-inch

• Overall more invasive and higher-cost repower

General Observations

• The QSK19 660 HP aligns closely with the S6R-Y3 at 1800 RPM, making it a practical and manageable repower candidate.

• The QSK19 750 HP can be addressed with the S6R2-Y3, but the lower operating RPM significantly increases repower complexity and cost.

• Cooling system configuration is a common driver of scope, with Mitsubishi engines requiring separate circuits and, in some cases, additional grid coolers.

• Repower feasibility is influenced not only by engine fit, but by drivetrain, cooling capacity, and long-term lifecycle expectations.