Cummins X15 delivers its best uptime and reliability yet

Engine nostalgia or not, Cummins’ latest X15 diesel is its most reliable heavy-duty engine yet, improving total cost of ownership for fleets and owner-operators. 

While older engines like the N14 still have plenty of fans, growing data shows the X15 has delivered the best uptime to date, resulting in more time on the road and a better bottom line.

First introduced in late 2016, the X15 has continued to undergo advancements including aftertreatment resulting in greater power and fuel economy along with lower emissions that meet strict state and federal regulations. 

Kristopher Ptasznik, Cummins Powertrain TCO & Consultancy Leader for North American Customer Support, noted that advanced designs have also bolstered reliability compared with earlier road warriors like the N14.

“I think it's important to note that the X15 is more reliable than the N14 in spite of modern emissions components that are put on it, even including the aftertreatment system that the N14 didn't have,” Ptasnik said. “We still touch it less. The N14 did not have high pressure common rail [fuel injection], EGR, VG turbos and yet the X15 has succeeded in reliability.” 

But seeing is believing. While the X15 shined on paper, Savage Trucking tested the engine on challenging grades while hauling 129,000 lb. loads in the Wasatch Range in central Utah.

“The real world is the lab that matters,” Savage Trucking Operations Manager Devon Simper said. 

Savage has 80 years of experience with what heavy loads are up against at 9,000 feet. 

Spec’d at a strong 605 horsepower and 2050 lb.-ft. torque, the X15 reliably conquered Wasatch time and again, earning the admiration of Simper and his drivers. 

Test results also showed the best fuel economy yet for Savage along with emissions that met stringent EPA standards. The performance soon led to an order for more than 200 X15s.
Steve Shaw, Technical Support Manager at Cummins Sales and Service North America, worked with Simper to help spec his trucks. 

“When a customer says prove it, we say, ‘Get in the truck,” Shaw said. 

Reliability requires rigid guidance in design

Over the years, Cummins engineers have steadily improved the X15 to the point that it has earned the highest percent-zero-touch rates and the lowest touches-per-thousand metrics to date.

“With eight years on a very mature hardware and software set, the engine is the best it has ever been,” Kyle Richardson, X15 Product Manager stated. 

The push to improve reliability was deliberate when the X15 entered full production in 2017, replacing the ISX15. 

“That 2017 design simplified what we had for the previous generation,” Richardson said. “Reliability was by far the most important attribute. Basically, we told everybody, if it doesn't have reliability in its name, do not bring it forward as an architectural feature that you want to pitch for 2017. When we jumped off on that foot, that set the stage for the product that we have today which has gained momentum.” 

Key X15 features include an in-house VGT turbocharger, a high-pressure XPI fuel system, a compact single-module aftertreatment system with longer maintenance intervals, and higher-capacity Fleetguard fuel and lube filters, all engineered to improve reliability and reduce unplanned downtime.

Improving uptime has sometimes meant passing on design changes that could improve a metric like fuel economy.

With decades of real-world and lab data, engineers have learned that keeping a truck on the road longer generates more revenue.

“When releasing a product, what are we considering to put on there? Could Cummins get better fuel economy today? Not if that means sacrificing reliability,” Ptasznik said. “Reliability is an important factor in TCO. All things considered equal, that is the key determining factor for why somebody is willing to pay more money upfront for a premium product.”

Reputation matters. If a truck is stuck at the shop, the best fuel economy in the world is not going to move a load that someone is counting on across the country. 

“A day of downtime can cost a customer hundreds to thousands of dollars. While it's down, you're still making that truck payment. You are still paying your driver, you are still paying the insurance on it and you are not utilizing your equipment,” Ptasznik said. “Uptime is extremely important. I think uptime is more important than fuel economy. I can buy a lot of gallons of diesel for $700.”

Trucks equipped with the Cummins X15 have earned a reputation for power and reliability which is continuing to attract buyers in the used truck market. 

“The X15 is a great performing product for the first user and is really driving secondary market value because it can be easily upgraded for additional power,” Richardson said.

Go ahead and break it

Aiming for the most reliable X15 yet through test cells and tracks has been critical, but as Simper made clear, real-world testing has been even more meaningful.

Variables like ambient temperature, weather conditions, traffic, driver habits, road surface, grades and fluctuations in fuel quality and duty cycles can push a powertrain out of its comfort zone. That is exactly what Cummins seeks.

Prior to the engine’s full production launch in 2017, Cummins expanded its lineup of testing partners to include operations that work their trucks particularly hard in demanding conditions.

That sometimes meant working with smaller fleets with smaller budgets.

“They were not easy conversations, but they were the right conversations and we've already seen the benefits from efficiency and reliability data generation,” Richardson said. “It’s really about how much data can you give the engineers? How many things can we break and pull on? We set the tone in 2017 and we've focused on carrying that forward.”

Real-world testing was not limited to the United States. Long before the X15 was released in North America, it went through punishing validation in Australia.

“Duty cycles there are significantly harder and more strenuous than in North America,” Ptasznik said. “As the Australians start to break our stuff that we think is rather good, we make improvements to that product to also carry into the North American market. 

That approach—testing hard, learning quickly and prioritizing reliability over incremental gains elsewhere—continues to guide X15 development. For Cummins, the goal remains unchanged: maximize uptime in the most demanding conditions so fleets and owner-operators can continue to count on the engine mile after mile.