Which Engine Models Are Used In Peterbilt Trucks & Who Makes Them?

The global economy depends heavily on tractor-trailers to deliver goods around the world, and Peterbilt has been a big player in the hauling industry since it was founded by T.A. Peterman in 1939. Peterman died in 1944, and the company was purchased by the Pacific Car and Foundry 14 years later. That company later changed its name to PACCAR, and is now responsible for making many of the engines that drive Peterbilt trucks. Big rigs have a green future, and Peterbilt is among many manufacturers that are turning to sustainable engine technology. However, its fleet today still relies heavily on diesel fuel. Diesel is popular among commercial freight haulers because diesel is more durable compared to gas engines.

Along with Peterbilt, PACCAR owns the Kenworth and DAF brands, and makes engines for a wide range of commercial trucks. The medium-duty PX-7 has a displacement of 6.7 liters, produces between 200 and 360 horsepower, and pushes out 800 pound-feet of torque. The PX-7 is available in the Peterbilt 348, which can also be outfitted with the PACCAR PX-9. This 8.9-liter powerhouse puts out between 260 and 450 horsepower and up to 1,250 pound-feet of torque. Moving up in the PACCAR line takes us to the MX-11, which is used in Peterbilt model 567 and 579 trucks. This 10.8-liter engine can put out as much as 430 horsepower and 1,650 pound-feet of torque.

The PACCAR MX-13 produces as much as 510 horsepower and 1,850 pound-feet of torque and is found in 567, 579, and 589 Peterbilt truck models. Peterbilt also uses the Cummins X15 in the model 589, which replaced the 389 for the 2024 model year. The manufacturer is also known for making light truck engines like its Cummins 6.7-liter turbodiesel inline-six engine, but even the high-output version of that engine is only capable of 420 horsepower and 1,075 pound-feet of torque. 

In comparison, the efficiency-optimized version of the X15 makes as much as 500 horsepower and 1,850 pound-feet of torque. For heavier loads, there's also a performance version that produces between 485 and 605 horsepower, and between 1,650 and 2,050 pound-feet of torque. Peterbilt's website also claims this engine has "the most powerful engine brake in the industry." 

The X15 debuted in 2017 as an updated version of the ISX15. The X15 is also used in mining and railroad applications and takes its label from an approximation of its 14.9-liter displacement. Two other Peterbilt models that use both PACCAR and Cummins engines are the 537 and 548, which can be outfitted with the PACCAR PX-7 or PX-9 for diesel power, or the Cummins L9N or B6.7N for buyers that want to run their trucks on natural gas.