PACCAR
PACCAR MX-13: Specs, Service Intervals, Lifespan & Common Problems
The PACCAR MX-13 is a 12.9-liter inline-six diesel, built for both the Peterbilt 579 and the Kenworth T680. PACCAR publishes a B10 design life of 1 million miles and a 5-year/500,000-mile major-components warranty. It also lists oil-and-filter intervals of up to 75,000 miles for line-haul with under 20% idle time.
Figures taken from the manufacturer's own published documents. Last reviewed September 23, 2026.
What are the PACCAR MX-13 specs?
| Configuration | Inline 6-cylinder |
|---|---|
| Displacement | 12.9 L |
| Bore × stroke | 130 mm × 162 mm |
| Power | 405–510 hp |
| Peak torque | 1,550–1,850 lb-ft |
| Dry weight | 2,500 lb |
| Oil system capacity | 42 U.S. qt |
| Governed speed | 2,200 rpm |
Commonly paired with the TX-12; see the transmission specs reference.
Fitted in the Peterbilt 579 and Kenworth T680; compare with the truck model specs.
How long does a PACCAR MX-13 last?
PACCAR states a B10 design life of 1 million miles (1.6 million km) for the MX-13. B10 is a reliability term. It means the mileage by which 10% of a group of engines is expected to have needed a major overhaul. So it's a statement about the early-failure tail, not the average engine. It's a design target, not a guarantee. Of the engines on this site, PACCAR and International are the two that print a design-life number on the spec sheets we reviewed.
Warranty, as the OEM lists it
- Base warranty: 2 years / 250,000 miles (400,000 km)
- Major components: 5 years / 500,000 miles (800,000 km)
- Extended protection plans are available
How often should you change the oil in a PACCAR MX-13?
PACCAR's published service intervals (2024 summary, EPA 2017/2021/2024 MX engines) for oil and filter, and for the fuel filter. The two use the same interval at each duty level. PACCAR recommends CK-4 oil. If you use CJ-4 oil in an EPA 2017 engine, PACCAR says the EPA 2013 intervals must be used instead.
| Duty cycle | Oil and filter interval |
|---|---|
| Normal / line haul, under 20% idle time | 75,000 miles |
| Normal / line haul, over 20% idle time | 50,000 miles |
| Severe / vocational duty | 30,000 miles |
- Coolant filter and DEF filter: 300,000 miles each.
- DPF cleaning: dry cleaning at 300,000 miles for normal line haul (150,000 for severe/vocational). Wet cleaning at 600,000 miles for normal line haul.
- PACCAR notes poor-quality fuel may need more frequent fuel filter service.
- Idle time is what moves you between the top two rows. Many drivers underestimate their real idle percentage. So check your ECM data instead of guessing.
Put your interval on a schedule with the maintenance scheduler.
What are the common problems with the PACCAR MX-13?
For the MX-13, repair-industry sources most often mention four areas, generally for higher-mileage engines.
- Fuel injectors
- Injector wear is one of the most frequently reported concerns on older model years. It shows up as rough running, hard starting, or higher fuel use.
- Turbocharger
- Turbo wear and malfunction are commonly reported. Repair sources place issues in roughly the 400,000–600,000-mile range.
- EGR valve and cooler
- EGR valve clogging and cooler wear are reported alongside turbo problems in the same mileage range.
- DEF and DPF regeneration
- DEF system faults and DPF regeneration issues are reported as a recurring annoyance. That is the same as every other SCR-equipped engine.
There is no public, independent failure-rate data for any heavy-duty diesel. So this section isn't a defect ranking. It lists the repair categories that shops and parts suppliers repeatedly report for this engine. Those sources sell repairs and parts, which is worth remembering. The same handful of systems (EGR, turbo, aftertreatment, fuel system) show up on every modern SCR-equipped diesel. Treat these as things to inspect on a used truck and to watch on your own, not as odds.
When a warning light comes on, decode it with the fault code lookup. Before you buy a used truck, run the VIN decoder and the used truck inspection checklist.
How does it compare with other heavy-duty engines?
Each engine guide on this site follows the same format and the same sourcing rule, so you can read them side by side.
Frequently Asked Questions
Is the PACCAR MX-13 a good engine?+
PACCAR backs it with a published 1-million-mile B10 design life and a 5-year/500,000-mile major-components warranty. Its 42-quart oil system supports long intervals, up to 75,000 miles for line-haul under 20% idle. The MX-13 is also lighter than the 15-liter engines. PACCAR cites up to 450 lb of weight savings. Whether one specific truck is a good buy still depends on its service history. The reported wear items (injectors, turbo, EGR) are common to the whole class.
What are the common problems with the MX-13?+
Repair-industry sources most often report fuel injector wear, turbocharger problems, EGR valve or cooler issues, and DEF/DPF regeneration faults, typically at higher mileage. Those sources sell repairs, and no independent failure-rate study exists. So treat this as an inspection list, not a probability.
How often should I change the oil in an MX-13?+
PACCAR lists 75,000 miles for line-haul with under 20% idle time. It lists 50,000 miles with over 20% idle, and 30,000 miles for severe or vocational duty. These assume CK-4 oil. Idle percentage is the deciding factor. So check your actual number.
Is the MX-13 the same in a Peterbilt 579 and a Kenworth T680?+
Yes — it's PACCAR's engine in both. The real differences between those trucks are cab, sleeper, and brand-specific factors, not the engine.
Sources
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Specs, intervals and warranty terms change by model year and configuration. Confirm the exact figures for a specific truck against the maker's current documents and your written warranty before you make a purchase or maintenance decision. Reported-issue information comes from repair and parts businesses, not from an independent failure study.
Free tools for a PACCAR MX-13 truck
Decode fault codes, keep service on schedule and check a truck before you buy.
- 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.