Engine Spotlight

John Baxter | March 01, 2011

Engine Innovation

Paccar’s MX stands out with unique design features.

Every trucker places a high value on torque and an engine’s ability to pull hills without needing to shift. Paccar’s new MX, which is close to full production at the company’s Columbus, Miss., manufacturing facility, has one unusual feature – fractured cap technology – that enhances this characteristic.

The Paccar MX is part of a three-engine series that includes the PX-6 and PX-8 medium-duty engines and the heavy-duty MX. Paccar, the owner of Peterbilt and Kenworth, also owns DAF, a European producer of diesel engines and trucks. The MX was originally developed to meet the Euro 4 and 5 emission standards and was then adapted for the U.S. market. It will be available only in Peterbilts and Kenworths.

The process involves the splitting the main bearing mounts and connecting rods. When they are reassembled, the mating of their rough edges produces an alignment more precise and rigid than standard rods or main bearing mounts, which have smooth mating surfaces.

The perfect alignment makes it possible to tune the engine to produce a “wide horsepower range and longer torque and power curves for more efficient operation,” according to the company. The technology also provides “improved bearing clearance, higher strength joints, increased uptime, and longer service life.”

Paccar says the engine is the only one in the marketplace that uses compacted graphite iron in both the block and cylinder head: “CGI is lighter and stronger than traditional gray iron and offers weight-sensitive users excellent horsepower-to-weight ratio to optimize payload,” a company report says. “The distinctive MX crankshaft reduces weight and increases power for quicker acceleration and smoother overall operation.”

Up to 75 percent stronger than gray iron, CGI is “200 percent more resistant to thermal fatigue,” the company says. That property contributes to a projected “industry leading” service life of 1 million miles for 90 percent of the engines produced, says Preston Feight, chief engineer for Kenworth Truck Co. “Using CGI in the block and head reduces weight and provides for a very high-strength, reliable and quiet engine,” he says.

Another unusual aspect of the design is the single, in-block camshaft, which is driven from the flywheel end of the engine to minimize noise and vibration. This layout uses highly developed unit injector pumps, along with sophisticated electronic control valves on both the pumps themselves and the injectors they feed to coordinate fuel delivery.

“We can achieve 36,000 psi at the injector tip,” Paccar says, “which allows for excellent fuel atomization and combustion, delivering superior fuel economy and low emissions.” Also, the fuel galleries are integrated into the cylinder head to reduce leaks, and improve reliability.

The camshaft operates the unit injector pumps, the four valves per cylinder, and the integral, camshaft-operated engine brake, which is rated at 465 hp, and allows a low total engine height for easier fit under hoods designed for ideal aerodynamics.

The engine’s integrated lubrication module combines filters, a thermostat and an oil cooler joined directly to the engine without external lines “to maintain oil quality and extend service intervals,” Paccar says. “The module includes an easy-to-access, cartridge-style oil filter to make service visits quicker and cheaper.”

The MX also features a fully encapsulated wiring harness mounted directly to the block, said to “protect wiring from the elements and remove stress from connectors” and result in optimum dependability in the electrical system.

“The oil filter module, which consists of a cartridge-style filter in combination with a centrifugal element, offers a maintenance interval of 40,000 miles,” Feight says. “The module is located forward on the passenger side of the engine for easy access during service. When the cover is loosened, oil in the filter module drains back into the oil pan, which significantly reduces the clean-up normally associated with an oil change. The fuel filters are located rearward on the driver’s side of the truck and are also well-placed for ease of service.”

Performance has been excellent, he notes. “Many customers have commented on how hard the engine pulls and have also commented on how quiet it is. We launched in June and have continued to increase production of the engine.”

Reported fuel economy, too, has been excellent. John Schmiedeke, co-owner and president of Taylor Transportation, an 18-truck auto hauler in Great Falls, Mont., says his fleet purchased a Kenworth T600 with a Paccar MX engine rated at 485 hp and 1,650 lb.-ft. of torque with a 9-speed transmission.

Schmiedeke drove the truck on a 500-mile trip and was pleased: “It holds speed when climbing hills and pulls real well. The engine sounds quieter than what I’m used to, more like a diesel pickup than an 18-wheeler. It’s one of the nicest trucks I’ve ever bought.”

The company’s other trucks have engines rated up to 600 hp. Because of high wind resistance when hauling cars, they get only 4.8 to 4.9 miles per gallon. However, Schmiedeke says, “The new T600 has gotten up to 5.9 mpg, way up from our other rigs.”


CONFIGURATION: Inline 6-cylinder, four valves per cylinder

INJECTION: Single in-block camshaft with electronically controlled unit injector pumps

ENGINE BRAKE: Integral, rated at 465 hp

DISPLACEMENT: 12.9 liters

BORE AND STROKE: 130 mm x 162 mm




TORQUE: 1,450-1,650 (1,550/1,750 multi-torque) lb.-ft.

DRY WEIGHT: 2,640 lb.


CHANGE INTERVALS: 40,000 miles for oil, oil filter and primary fuel filter

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