If you have read our Peterbilt 579 guide, a lot of this will be familiar. The trucks are cousins. Where they differ, we say so.
T680 or 579? They are not the same truck
Both are PACCAR products built on shared engineering. Both take the MX-13 or the Cummins X15. The differences that actually matter to a used buyer:
| Kenworth T680 | Peterbilt 579 | |
|---|---|---|
| Cab and interior | Different layout and trim | Different layout and trim |
| Driver preference | Strong, and regional | Strong, and regional |
| Used supply | Deep | Deeper |
| Powertrain | Same options | Same options |
| Service network | PACCAR | PACCAR |
The honest answer is that the choice between them is mostly about driver preference, resale in your particular market, and which specific truck is in better condition. Do not buy a worse T680 over a better 579 because of the badge, or the other way around.
Generations
| Period | What to know |
|---|---|
| 2013 to 2020 | Original T680. EPA 2013 and EPA 2017 calibrations depending on year. Deep used supply, and where most current used inventory sits. |
| 2021 onward | Next-generation T680 with revised aerodynamics, interior, and electrical architecture. Some 2021 to 2022 units were built under pandemic-era supply constraints, and operators report more variability in those builds. |
That variability note is anecdotal, drawn from operator forums rather than published data. Treat it as a reason to inspect carefully, not as a rule.
The MX-13 coolant crossover tube
This is the one item that separates a T680 buyer who knows what they are doing from one who does not.
The coolant crossover tube runs between the cylinder heads on the PACCAR MX-13. Its sealing surfaces degrade over time, and the failure is progressive rather than sudden. Mechanics who work on these regularly describe it as a wear item that affects the engine eventually rather than a defect that affects some units.
What it looks like: slow, unexplained coolant loss with no visible puddle. Coolant residue or staining at the top-center or rear of the engine. The owner topping off coolant and not knowing why.
When: commonly reported after 300,000 miles.
Why it matters when buying: an owner who has been topping off coolant for six months may describe the truck as having no problems. The ECM will not necessarily flag it. This is exactly the kind of thing an inspection catches and a test drive does not.
What to do: check coolant level, look for staining at the top-center and back of the engine, and ask directly whether the crossover tube has been replaced with the updated PACCAR part. On a truck over 300,000 miles with the original tube, factor a replacement into your budget whether or not it is leaking yet.
What else breaks
Multiplex electrical faults. The T680 has a complex electrical architecture and the characteristic failure mode is a fault that presents in one place and originates in another. Symptoms cascade: several warning lights at once, often for systems that turn out to be fine. Diagnosis time is the expense, not parts.
DPF regeneration failures. The most common single complaint. Aggravated by stop-and-go duty cycles where regens do not complete. Ask when the DPF was last cleaned and what the duty cycle was.
DEF system faults. Quality sensor failures, doser issues, contamination. Common across the platform and across brands.
Cooling system. The MX-13 runs hot under load. Clogged radiators and failed thermostats show up as temperature climbing on grades. Related to but distinct from the crossover tube issue.
Turbocharger and VGT actuator. Boost pressure faults and exhaust pressure sensor codes are frequently reported. Power loss and black smoke are the symptoms.
Air system leaks. Suspension bags and brake chambers. Routine, but they are DOT items and they are a direct deduction from what you should pay.
What to check before you buy
- Pull the ECM report. Engine hours, idle percentage, fault history, derate events.
- Check coolant level and look for crossover tube symptoms. See above. This is the T680-specific item.
- Ask whether the crossover tube has been replaced and whether the updated part was used.
- Verify aftertreatment history. Last DPF cleaning, DEF system repairs, any SCR work.
- Have the electrical system scanned properly, not just read for active codes. Ask for inactive and intermittent faults too.
- Check the engine model year against the truck year. Not always the same, and for California work above 26,000 pounds GVWR the engine year is what counts.
- Run the VIN through NHTSA and confirm any open recalls have been remedied. PACCAR has issued campaigns affecting T680s across several model years.
- Inspect the frame and wiring for corrosion. See our guide to frame rust.
- Get a third-party inspection. Not the seller’s inspector.
Is a used T680 a good buy in 2026?
For on-highway work, yes, with the crossover tube factored in. The platform is proven, the used supply is deep, and PACCAR service coverage is broad.
The market context supports it. New Class 8 sleepers are past $170,000 and remaining 2026 build capacity was oversubscribed through the summer, so buyers who need iron this year are shopping used. A documented T680 with known aftertreatment and cooling history is a straightforward purchase.
Walk away from the one with slow coolant loss the owner cannot explain.
Frequently asked questions
Is the Kenworth T680 a good truck? It is one of the most widely used aerodynamic Class 8 tractors in North America, with deep used supply and broad PACCAR service coverage. Condition, engine choice, and maintenance history matter more than the model.
What are the most common Kenworth T680 problems? The most frequently reported are the PACCAR MX-13 coolant crossover tube, multiplex electrical faults, DPF regeneration failures, DEF system faults, cooling system issues under load, and turbocharger or VGT actuator problems.
What is the MX-13 coolant crossover tube problem? The coolant crossover tube runs between the cylinder heads on the PACCAR MX-13. Its sealing surfaces degrade with age and mileage, commonly after 300,000 miles, producing slow unexplained coolant loss and staining at the top-center or rear of the engine. An updated PACCAR replacement part is available.
Is the T680 or the Peterbilt 579 better? They share powertrain and much of their engineering, so the difference is largely cab, driver preference, and regional resale. Condition of the specific truck matters far more than the choice between the two.
How many miles will a Kenworth T680 last? Well-maintained Class 8 trucks routinely exceed 1,000,000 miles. The more useful question is which major service events have already been completed.
Current Kenworth T680 inventory at Charter
Every Charter T680 comes with a third-party inspection report covering cooling system and aftertreatment condition. See all inventory or call 707-669-6202.
