Engine comparison
Detroit DD15 vs PACCAR MX-13: Specs, Weight, Intervals and Warranty Compared
The Detroit DD15 is a 14.8-liter engine and the PACCAR MX-13 is a 12.9-liter one. The makers' own sheets put the MX-13 about 218 lb lighter (2,500 lb dry versus 2,718 lb). PACCAR is the only one of the two that prints a design-life figure (B10 of 1 million miles). It also prints a major-components warranty of 5 years or 500,000 miles. Detroit covers major components from month 25 through month 60 or 500,000 miles, parts only. Both list a 75,000-mile oil interval at the top of their duty ranges. There is no independent head-to-head on fuel economy or reliability. So the pick depends on which truck you're buying.
Figures taken from the manufacturers' own published documents. Last reviewed September 24, 2026.
DD15 vs MX-13: side-by-side specs
| Spec | Detroit DD15 | PACCAR MX-13 |
|---|---|---|
| Displacement | 14.8 L (906 cu in) | 12.9 L |
| Bore × stroke | 139 mm × 163 mm (5.47 in × 6.42 in) | 130 mm × 162 mm |
| Power | 425–505 hp (DD15 family) | 405–510 hp |
| Peak torque | 1,550–1,850 lb-ft | 1,550–1,850 lb-ft |
| Dry weight (each maker's own figure) | 2,718 lb (1,233 kg) | 2,500 lb |
| Oil system capacity | 45 qt (43 L) service fill | 42 U.S. qt |
| Published B10 design life | Not stated on the Gen 5 spec sheet | 1 million miles (1.6 million km) |
| Base warranty | Not detailed on the sheet reviewed | 2 years / 250,000 miles |
| Major-component warranty | Months 25–60 or 500,000 mi; parts covered, labor not | 5 years / 500,000 miles |
| Oil interval, top duty band | 75,000 mi (over 60,000 annual miles, over 7 mpg) | 75,000 mi (line haul, under 20% idle time) |
| Oil interval, mid band | 60,000 mi (long-haul, 6.0–6.9 mpg) | 50,000 mi (line haul, over 20% idle time) |
| Oil interval, severe duty | 35,000 mi (under 5 mpg, up to 30,000 annual miles) | 30,000 mi (severe / vocational) |
| Trucks | Freightliner Cascadia | Peterbilt 579 and Kenworth T680 |
| Transmission it's paired with | Detroit DT12 | PACCAR TX-12 |
Full detail for each engine: Detroit DD15 guide and PACCAR MX-13 guide.
What actually decides DD15 vs MX-13?
We don't name a winner: there's no independent, like-for-like study of fuel economy or reliability for these engines. These are the facts that decide it for a given truck and duty cycle.
- The truck comes with the engine
- The DD15 is Detroit's engine for the Freightliner Cascadia. The MX-13 is PACCAR's engine for the Peterbilt 579 and Kenworth T680. For most buyers the real decision is the truck and its dealer network. The engine follows from it.
- Size and weight are real, published differences
- The DD15 is the larger engine (14.8 L versus 12.9 L). Detroit's sheet lists it about 218 lb heavier on each maker's own dry-weight basis. PACCAR states up to 450 lb of savings against 15-liter engines in its own literature. That is a manufacturer claim, and the basis of comparison is PACCAR's. So read it as the direction, not an exact figure for your truck. Whether weight matters depends on how close you run to the legal limit.
- Peak numbers overlap almost completely
- Both list peak torque of 1,550–1,850 lb-ft and similar horsepower ranges. So don't shop on the top-line numbers. Compare the specific rating installed in the truck you're looking at, since each engine is sold in several tunes.
- Only one publishes a design-life number, and it's a design target
- PACCAR's 1-million-mile B10 means it expects 10% of engines to need a major overhaul by that mileage. It's a design target for the early-failure tail, not a guarantee or an average. Detroit's sheet doesn't print an equivalent. That doesn't mean the DD15 is worse. It means the two makers document differently. The written warranty on the specific truck is the firmer comparison.
Put your interval on a schedule with the maintenance scheduler. Decode warning lights with the fault code lookup. Before you buy a used truck, run the VIN decoder and used truck inspection checklist.
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Frequently Asked Questions
Which is better, the DD15 or the MX-13?+
There isn't an independent head-to-head study of reliability or fuel economy for these two engines. So we don't name a winner. Here is what's published. The DD15 is larger (14.8 L versus 12.9 L) and heavier. The MX-13 states a 1-million-mile B10 design life and a 5-year/500,000-mile major-components warranty. Both list peak torque of 1,550–1,850 lb-ft. Your decision is largely which truck, Cascadia or 579/T680, fits how you run.
Is the MX-13 lighter than the DD15?+
On each maker's own published sheet, yes. PACCAR lists 2,500 lb dry for the MX-13 and Detroit lists 2,718 lb for the DD15. That is roughly a 218 lb difference. Each maker measures on its own basis. So treat it as an indication, not a scale-verified gap.
How do the oil change intervals compare?+
PACCAR lists 75,000 miles for line haul under 20% idle time, 50,000 miles over 20% idle, and 30,000 for severe or vocational duty. Detroit lists 75,000 for efficient long-haul over 7 mpg, 60,000 for long-haul, 45,000 for short-haul and 35,000 for severe duty. PACCAR keys off idle percentage. Detroit keys off mpg and annual miles. So check your own numbers against each table.
Which has the better warranty?+
PACCAR prints a 5-year/500,000-mile major-components warranty and a 2-year/250,000-mile base warranty. Detroit's sheet lists major-component coverage from month 25 through month 60 or 500,000 miles, with parts covered and labor not. The two are worded differently. So compare the written terms for the exact truck, not the headline mileage.
Sources
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Specs, intervals and warranty terms change by model year and configuration. Power and torque ranges are from our engine reference. Confirm exact figures for a specific truck against the manufacturer's current documentation and your written warranty before buying or setting a service schedule.
Free tools for a DD15 vs MX-13 decision
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- Diesel Fault Code Lookup (SPN/FMI)Decode the SPN/FMI fault codes this engine reports.
- Preventive Maintenance SchedulerTrack oil and filter intervals by odometer for your duty cycle.
- Breakdown Cost EstimatorEstimate what a breakdown costs in repairs and lost revenue.
- Truck Breakdown TriageIf this engine shows a red lamp or overheats, see if you should stop now.