Quick answer: Detroit, Cummins and PACCAR all build heavy-duty diesels that can run a long time in a used Class 8 truck. The differences come down to where each engine is installed, how much power it offers, and who can service it near you. Detroit engines come mostly in Freightliner and Western Star trucks, PACCAR MX engines in Kenworth and Peterbilt, and Cummins X15 engines across several brands. For a used truck, the maintenance history and condition of the specific engine matter more than the badge on the valve cover.
Key takeaways
- The Detroit DD15 Gen 5 is a 14.8 litre engine rated at 425 to 505 hp and 1,550 to 1,850 lb-ft, according to Detroit's product page.
- Cummins X15 ratings run from 400 to 605 hp and 1,450 to 2,050 lb-ft across the Efficiency, Performance and Productivity series, per International's 2024 X15 listing.
- The PACCAR MX-13 is a 12.9 litre engine rated at 405 to 510 hp and 1,550 to 1,850 lb-ft, according to Peterbilt's 2024 spec sheet.
- Repair and maintenance averaged 21.5 cents per mile in 2025, according to the American Transportation Research Institute (ATRI), so a well-chosen engine affects your costs every month.
- Service access near your lanes, emissions system condition and documented oil analysis usually tell you more than brand reputation.
- Lenders look at the truck's age, kilometres and condition alongside your cash flow. Startups need at least 6 months of revenue in business bank statements.
The three engine families at a glance
All three manufacturers build engines that meet current EPA and Transport Canada emissions rules, and all three have been refined over several generations. They differ in how they reach the market.
Detroit is part of Daimler Truck North America. Its DD13, DD15 and DD16 engines are designed to work with Detroit's own DT12 automated transmission and axles, and they are found mainly in Freightliner and Western Star trucks.
Cummins sells engines to many truck builders. You will find the X15 in International, Peterbilt, Kenworth, Freightliner and others, depending on the model year and spec. That wide footprint is a big part of why so many independent shops know the engine well.
PACCAR builds the MX-11 and MX-13 for its own Kenworth and Peterbilt trucks, usually paired with PACCAR's TX-12 automated transmission. If you're weighing those two brands, our Kenworth vs Peterbilt used truck comparison covers the cab and chassis side.
Published ratings compared
| Engine | Displacement | Horsepower | Torque | Usually found in |
|---|---|---|---|---|
| Detroit DD15 Gen 5 | 14.8 L | 425 to 505 hp | 1,550 to 1,850 lb-ft | Freightliner, Western Star |
| Cummins X15 (2024, all series) | Check data plate | 400 to 605 hp | 1,450 to 2,050 lb-ft | International, Peterbilt, Kenworth, Freightliner and others |
| PACCAR MX-13 (2024) | 12.9 L | 405 to 510 hp | 1,550 to 1,850 lb-ft | Kenworth, Peterbilt |
Ratings are from each manufacturer's or truck builder's published material for recent model years. Older engines in the used market may have different ratings, so check the engine data plate and the ECM settings on the truck you are looking at.
Power and the work you do
Horsepower and torque only matter in relation to your loads and your routes. A dry van running flat highway in southern Ontario has different needs from a logging truck in the BC Interior.
- Cummins offers the highest published ratings of the three, up to 605 hp and 2,050 lb-ft in the Productivity series. That makes the X15 a common pick for heavy haul, logging and other high-weight work.
- Detroit's DD15 covers most linehaul and regional work. Detroit also sells the larger DD16 for heavier applications.
- The PACCAR MX-13 covers similar ground to the DD15 with a smaller displacement. PACCAR markets it heavily for linehaul fuel economy.
Before you shop, write down your typical gross combination weight, your worst grades and how much time the truck spends idling. Then find engines rated for that work. Paying for a 600 hp heavy-haul engine you will never use can mean a higher purchase price and more fuel burned.
Fuel use
Fuel is one of the largest line items for any carrier. ATRI's 2025 operational costs update put total marginal costs at a record $2.336 per mile, with repair and maintenance alone at 21.5 cents per mile.
Detroit and PACCAR both lean on integrated powertrains. When the engine, transmission and axle come from one maker, the software can coordinate shift points and engine speed closely. Cummins works with several transmission and chassis partners, so real-world fuel use depends more on how the truck was spec'd.
In practice, the spec and the driver change fuel use as much as the engine brand does. Rear axle ratio, tire choice, aerodynamics, idle time and speed all move the number. When you compare two used trucks, ask for fuel records if the seller kept them, and compare trucks with similar specs.
Service access and parts
A truck that sits waiting for parts is not earning anything, and in Canada distance to the nearest qualified shop can be a real problem outside the major corridors.
| Factor | Detroit | Cummins | PACCAR |
|---|---|---|---|
| Main dealer network | Freightliner and Western Star dealers | Cummins distributors plus many truck dealers | Kenworth and Peterbilt dealers |
| Independent shop familiarity | Good on newer DD engines, varies by region | Very wide, many independents work on X15 | Growing, still more dealer-focused |
| Diagnostic software | Brand-specific tools | Brand-specific tools, widely licensed | Brand-specific tools |
| What to check before buying | Distance to dealer on your lanes | Which shops near you handle major work | Distance to Kenworth or Peterbilt dealer |
Map the shops along your regular routes before you commit. A Cummins engine may be easier to service in a small town with only an independent shop, while a Detroit or PACCAR engine is well supported if you run lanes with dealers on them.
Warranty and service intervals
Engine makers publish base and extended warranty terms, and those terms can transfer with a used truck if they are still active. Peterbilt's 2024 MX-13 spec sheet lists a base warranty of 2 years or 400,000 km and major component coverage of 5 years or 800,000 km. The same document cites oil change intervals of up to 75,000 miles in some duty cycles. Always confirm what coverage remains on a specific truck by running the serial number through a dealer. If coverage is close to expiring, extended warranty financing can spread the cost of a new plan over monthly payments.
Reliability and what drives repair costs
All three brands publish design life figures and warranty terms, but no independent body publishes a neutral reliability ranking of Detroit vs Cummins vs PACCAR. Be careful with online claims that one brand "always" outlasts the others. Reputations often come from a single troubled model year.
What actually drives repair costs on a used engine:
- Oil change history and oil analysis results, which show wear metals, coolant or fuel in the oil.
- Emissions system care, including diesel particulate filter (DPF) cleaning, regeneration history and diesel exhaust fluid (DEF) system faults.
- Idle time, which builds soot and loads the aftertreatment system.
- Duty cycle. A truck that pulled heavy loads in the mountains has worked harder than one that ran light freight on flat highway.
- Prior major repairs, such as an in-frame overhaul, EGR cooler or turbo replacement.
Our guide to checking diesel engine health on a used truck walks through these checks in more detail, and how to read mileage and engine hours explains why both numbers matter.
Emissions systems on used trucks
Trucks built after the 2007 and 2010 EPA standards carry DPF and selective catalytic reduction (SCR) systems. Neglected aftertreatment is one of the most common reasons a cheap used truck turns expensive. Pull the fault code history, ask when the DPF was last cleaned or replaced, and look for repeated forced regenerations. Our post on emissions standards in Canadian trucking explains what changes from one model year to the next.
Overhaul and repair planning
Every engine eventually needs major work, and at that point you have to decide whether the truck is worth the repair. Signs include rising oil consumption, blow-by, low compression, coolant loss and power loss. Our post on signs your used truck needs an overhaul covers the warning signs.
When you price a used truck, set aside a reserve for major work based on the engine's kilometres and history. For cost ranges, see semi truck engine repair costs in Canada. If an overhaul is needed, engine rebuild and replacement financing or repair and breakdown financing can spread the cost instead of draining your operating account. We also cover PACCAR and Volvo engine rebuild financing and heavy truck engine overhaul loans.
Choosing by operation type
| Operation | Engines often chosen | What to focus on |
|---|---|---|
| Long-haul dry van or reefer | Detroit DD15, PACCAR MX-13, Cummins X15 Efficiency | Fuel use, idle time, integrated transmission |
| Heavy haul, logging, mountain routes | Cummins X15 Productivity, Detroit DD16 | Torque, cooling, engine brake |
| Regional and day cab | Detroit DD13, PACCAR MX-11, Cummins X15 | Weight, service access, purchase price |
| Rural or remote lanes | Often Cummins for shop coverage | Shops and parts within range of your routes |
Use this as a starting point. A well-maintained engine from any of the three will usually serve better than a neglected one from your preferred brand.
How engine choice affects financing
Lenders don't usually set terms by engine brand. They look at the truck as collateral (year, kilometres, condition and resale value) and at your ability to make payments. That said, a truck with a documented engine history tends to be easier to finance, because it reduces the risk of a breakdown that hurts both the truck's value and your cash flow.
Expect a lender to ask for:
- a bill of sale or dealer invoice with the VIN
- photos and, for older units, an inspection report
- business bank statements, usually the last 3 to 6 months
- your driver's licence, operating authority and insurance details
An equipment loan gives you ownership from day one. An equipment lease can lower upfront cash and may suit fleets that turn over trucks every few years. Our complete guide to used truck financing in Canada compares both, and used truck financing with bad credit covers files with credit challenges.
What we see on real files
A few patterns show up again and again on used truck files. Buyers who bring oil analysis reports and full service records tend to get through lender review with fewer conditions. Older trucks with very high kilometres often draw shorter terms or a larger down payment request, whatever the engine. Private sales move faster when the seller has lien search results and a clean ownership history ready. And owner-operators who budget a repair reserve from the start handle the first major repair without falling behind on payments.
Newer businesses can qualify too. If you have at least 6 months of revenue in your business bank statements, we can take your file to lenders who work with startups.
Pre-purchase checklist
- Confirm the engine model, serial number and rating from the data plate and ECM.
- Run the serial number with a dealer to check open recalls and remaining warranty.
- Pull ECM data: idle percentage, fuel use, fault history and regeneration counts.
- Get an oil sample analysed by a lab.
- Ask for service records, including any overhaul, turbo, EGR or aftertreatment work.
- Have an independent mechanic inspect the truck, including a dyno test if possible.
- Do a lien search before you pay. Buying at auction? Read auction financing for used trucks first.
- If the truck is coming from the US, review importing a used truck from the US to Canada.
Frequently asked questions
Which engine is best for a used semi truck?
There is no single best engine. Detroit, Cummins and PACCAR all build capable diesels. Match the engine's rating to your loads and routes, and pick the specific truck with the best documented maintenance history.
Which has the most horsepower?
Among the engines compared here, the Cummins X15 Productivity series has the highest published ratings, up to 605 hp and 2,050 lb-ft, according to International's 2024 listing.
Is a PACCAR MX-13 harder to service than a Cummins?
PACCAR engines are serviced mainly through Kenworth and Peterbilt dealers, while Cummins engines are supported by Cummins distributors and many independent shops. Which one is easier depends on the shops along your routes.
Does the engine brand affect my financing approval?
Not usually on its own. Lenders focus on the truck's age, kilometres, condition and value, plus your business cash flow and credit. Good engine records can make the review smoother. Approval and terms are never guaranteed.
Can I finance an engine overhaul on a truck I already own?
Yes, engine repair and overhaul financing is available for qualifying commercial trucks. You can also look at refinancing or a sale-leaseback to free up equity in a paid-off truck.
How many kilometres is too many for a used engine?
It depends on the engine, duty cycle and history. A high-kilometre engine with a documented in-frame overhaul can be a better buy than a lower-kilometre engine with no records.
Tools and next steps
Estimate payments with our equipment financing calculator, or compare options with the loan vs lease comparison. Look up terms like total cost of ownership and down payment in our glossary. Explore truck and trailer financing, our transportation and trucking industry page, and our Freightliner vs Peterbilt comparison. For fleets with several units, the fleet repair program can help with ongoing maintenance costs.
Finance your next used truck
Mehmi Financial Group works with over 50 lenders across Canada and the USA, including lenders who finance used Class 8 trucks and engine repairs. Call 1-833-863-4644 or apply online to compare your options.
Sources
- Detroit (Daimler Truck North America), Detroit DD15 engine, accessed November 2026.
- International Motors, Cummins X15 engine (2024 series), accessed November 2026.
- Peterbilt Motors, PACCAR MX-13 spec sheet, 2024.
- American Transportation Research Institute, An Analysis of the Operational Costs of Trucking: 2026 Update, as reported by HDT Trucking Info, July 15, 2026.
Written by Jodhbir Mehmi. Reviewed under our editorial standards. Updated November 2026.