Cummins
Cummins X12: Specs, Service Intervals, Lifespan & Common Problems
The Cummins X12 is an 11.8-liter inline-six diesel, smaller than the Cummins X15. Cummins lists 350–500 hp and 1,250–1,700 lb-ft. Dry weight is 2,050 lb. Its 2021 brochure sets the oil drain interval by fuel economy, from 40,000 miles for severe duty up to 75,000 miles for light duty. The X12 was also part of a 2021 fuel tube safety recall.
Cummins published the Cummins X12 figures in its own documents. Last reviewed November 3, 2026.
What are the Cummins X12 specs?
| Configuration | Inline 6-cylinder |
|---|---|
| Displacement (Cummins motorhome sheet) | 11.8 L (720 cu in) |
| Power | 350–500 hp |
| Peak torque | 1,250–1,700 lb-ft |
| Clutch engagement torque | 800 lb-ft |
| Dry weight | 2,050 lb (930 kg) |
| System weight, depending on configuration | 2,241 lb (1,017 kg) |
| Rating series | Efficiency ratings run 350–455 hp for line and regional haul. Productivity ratings run up to 500 hp for vocational and refuse. |
| Oil capacity with filter (Cummins motorhome sheet) | 45 qt (43 L) |
Commonly paired with the Endurant HD; see the transmission specs reference.
Fitted in the Freightliner Cascadia and Western Star, Autocar, Oshkosh and Terex vocational trucks; compare with the truck model specs.
How long does a Cummins X12 last?
Cummins' X12 truck brochure does not state a B10 design-life mileage, so this page does not print one. Cummins' motorhome sheet says the X12 platform has more than 2 billion miles of real-world experience. That adds up many engines. It says nothing about how long one engine lasts.
Warranty, as the OEM lists it
- Not stated in the X12 truck brochure. Coverage depends on the truck brand and how the engine was ordered. Confirm it in writing for the specific truck
- Cummins' motorhome sheet lists a 5-year/100,000-mile base warranty. That is an RV term, not a truck term
Cummins X12 oil capacity: how much oil does it hold?
45 quarts (43 liters) with the filter, as Cummins lists it on its X12 motorhome sheet. Cummins' X12 truck brochure does not list a capacity, and a truck oil pan can differ. Check your operator's manual before you buy oil.
Capacity is how much oil goes in. The interval is how often you change it. The next section covers the interval.
How often should you change the oil in a Cummins X12?
These oil intervals come from Cummins' X12 truck brochure for the 2021 X12. They are set by fuel economy. Cummins says to use the next lower interval when idle time plus PTO time is over 40% for short-haul, normal or light duty. Other X12 setups can differ, so use the guide for your engine.
| Duty cycle | Oil and filter interval |
|---|---|
| Vocational | 1,500 hours or 18 months |
| Severe (3–4.9 mpg) | 40,000 miles |
| Short-haul (5.0–5.9 mpg) | 50,000 miles |
| Normal (6.0–6.9 mpg) | 60,000 miles |
| Light (over 7.0 mpg) | 75,000 miles |
- With its OilGuard program, Cummins lists longer intervals. For light duty it lists up to 100,000 miles.
- Fuel filter: 30,000 miles for severe duty, 40,000 for short-haul, 50,000 for normal and 60,000 for light duty. Vocational is 1,500 hours. Cummins lists longer fuel filter intervals with a remote-mount filter.
- Cummins lists 300,000 miles for DEF service and for the valvetrain.
- DPF ash cleaning runs 300,000–400,000 miles for severe and short-haul duty. It runs 400,000–600,000 for normal and 600,000–800,000 for light duty. Cummins recommends a Cummins remanufactured DPF at that service.
Put your Cummins X12 interval on a schedule with the maintenance scheduler.
What should you check before you buy a used truck with a Cummins X12?
- Ask for service records and compare them with the oil interval table above.
- Get the warranty terms in writing for that exact truck. The documents we read do not state them.
- Check recall status by VIN. This engine has a recall on record, described below.
What are the common problems with the Cummins X12?
The one X12 problem we can back with a government document is a safety recall. Beyond that, we found no repair report specific to the X12 that we could rely on. Search results mixed it with other Cummins engines. Read the recall below, and check the VIN for recall status on any used X12.
Fuel tube recall (NHTSA 21E-099, December 2021)
Cummins recalled 10,938 X12 engines because the fuel tubes to cylinders 4, 5 and 6 could crack and leak fuel at high pressure. A leak near an ignition source can cause a fire. The recall covers engines built from April 2016 through early November 2021. Cummins' filing reports one fire in September 2021, traced to a leak at cylinder 5, and no injuries. The fix replaces the tubes for cylinders 4, 5 and 6 and adds vibration isolators. Engines with 75 miles or less get the isolators only.
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 theCummins X12 next to the other engines.
Frequently Asked Questions
How much oil does a Cummins X12 hold?+
45 quarts (43 liters) with the filter, as Cummins lists it on its X12 motorhome sheet. Cummins' X12 truck brochure does not list a capacity, and a truck oil pan can differ. Check your operator's manual before you buy oil. That tells you how much oil to buy. The service interval tells you when to change it, so read both.
How many liters is a Cummins X12?+
Cummins' X12 motorhome sheet lists 11.8 liters (720 cubic inches). The truck brochure gives the engine's size class as 10 to 13 liters but no exact figure. Cummins pages for other markets round it to 11.9 liters.
How much horsepower does a Cummins X12 have?+
Cummins lists 350 to 500 hp and 1,250 to 1,700 lb-ft of torque. The Efficiency ratings for line and regional haul top out at 455 hp. The Productivity ratings for vocational and refuse work go up to 500 hp.
When did the Cummins X12 come out?+
NHTSA's recall report lists X12 engines built as early as April 26, 2016. Cummins' brochure covers the 2021 X12, which it pairs with the Endurant HD transmission in the Freightliner Cascadia.
Is the Cummins X12 a good engine?+
Cummins lists a low dry weight and long oil intervals for light duty. It states no design-life mileage, and we found no engine-specific repair data we could rely on. It had one safety recall in 2021, for fuel tubes. So judge a specific truck by its service record and its recall status.
How often should I change the oil in a Cummins X12?+
Cummins' 2021 brochure lists 40,000 miles for severe duty (3–4.9 mpg), 50,000 for short-haul (5.0–5.9 mpg), 60,000 for normal (6.0–6.9 mpg) and 75,000 for light duty (over 7.0 mpg). Vocational use is 1,500 hours or 18 months. Use the next lower interval if idle plus PTO time is over 40%.
Is the X12 the same as the ISX12?+
No. Cummins' brochure compares the X12 with the ISX12. It cites a new engine brake with more stopping power and a lighter single-module aftertreatment system. Treat reports about the older ISX12 as a different engine.
Sources
Run a Cummins X12 truck? Let a dispatcher handle the rest.
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Specs, intervals and warranty terms for the Cummins X12 change by model year and configuration. Confirm the exact figures for a specific truck against Cummins'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 Cummins X12 truck
Decode Cummins X12 fault codes, keep its service on schedule and check a truck before you buy.
- Diesel Fault Code Lookup (SPN/FMI)Decode the SPN/FMI fault codes the Cummins X12 reports.
- Preventive Maintenance SchedulerTrack Cummins X12 oil and filter intervals by odometer for your duty cycle.
- Breakdown Cost EstimatorEstimate what a Cummins X12 breakdown costs in repairs and lost revenue.
- Truck Breakdown TriageIf the Cummins X12 shows a red lamp or overheats, see if you should stop now.