Paccar MX-13 380E (F & E)

After ten years of development and roughly a billion dollars of investment, PACCAR unveiled the MX line in February 2010; the MX-13 entered series production in Kenworth and Peterbilt trucks from summer 2010, backed by a dedicated engine plant built in Mississippi. It replaced third-party engines — including Cummins and Caterpillar units — previously used in PACCAR's own brands.

The MX-13 is now the standard long-haul engine for Kenworth and Peterbilt in North America; PACCAR has publicized delivery of its 100,000th North American-built MX-13, underscoring how broadly it has been adopted.

Like the whole MX family, the MX-13 uses a one-piece engine block with cylinder bores machined directly into it rather than replaceable wet liners, increasing rigidity but making repairs more involved in case of damage than on liner-equipped engines. Like other heavy long-haul diesels, it is tuned for a low rated speed with a broad torque plateau, cutting fuel consumption at steady cruising speed, unlike higher-revving engines built for distribution work.

Because it's a relatively young in-house design with high parts integration, buyers of a used MX-13 should check the documented SCR/EGR service history, since PACCAR has repeatedly revised engine calibration over the model's production run.