Combustion v. Compression

Do medium-duty trucks run better on diesel engines or gasoline power? If you only consider the price at the pump, you may be missing the bigger picture Web Extra!

"They did find some preference for gas in rural areas, neighborhoods where noise was a concern," Niekamp says. "The companies that prefer gas don't intend to keep their vehicles as long. Or they have smaller, lighter-duty trucks, such as Class-4, that tend to skew higher towards a preference for gas than Class-5.

"But Sterling's conclusion from this research was that customers in the medium-duty segment by and large do prefer a diesel engine. They came away convinced, as we were, that the strategy for our customers was the right one."


To Brad Pugh, Ram Chassis Cab product planner for Chrysler LLC Commercial Vehicles, the reasons for diesel's popularity in his medium-duty product are easy to grasp.

"The diesel is as popular as it is, number one, because of the way it performs," he says. "Number two, in a very close second, is the name Cummins on the badge.

"With the Cummins you get best-in-class fuel efficiency," he says, "so you're saving money at the pump when you're hauling heavy loads, and you're able to develop all your torque at super-low engine rpms. So, at 1,600 rpm, we already have all our engine torque, which is 610 lb-ft.

"You compare that to a gas engine, where your torque curve is steep--it's more like a mountain slope, as opposed to a plateau that you get with a diesel engine," he explains. "So, you get maximum pulling power for trailer towing, for the heavy loads that a Class-3, 4 or 5 sees. And you're able to get that right off the line."

Pugh also points out that diesel trucks generally have higher resale value: "If you look at the historical prices of used trucks, the ones with diesel engines will hold their value a little bit better, and you'll get a higher return when you have to replace that truck."


Although one reason cited by Craig Joost with 1-800-GOT-JUNK for eschewing diesel engines was concern about the regeneration process of the diesel particulate filter (DPF), Pugh doesn't see this as a significant issue.

"The technology shouldn't be as scary as it is to the customer, especially in a Class-4 or 5 truck where, right now, you don't have to remove the particulate trap to clean it," Pugh says. "We've worked hard with Cummins to calibrate it so that it actually does a cleansing process when it gets close to full, with pressure sensors in there to monitor how full the particulate trap is. Once it reaches a certain point, it goes through a regen process that cleans it out and allows airflow back into the system and restores it to its normal operating state. But there's not a whole lot of extra maintenance required because of that system, and I'm surprised that people would be scared off by it."

In the end, Isuzu's commitment to offering its customers a gasoline option is just as courageous as Chrysler LLC's commitment to a diesel-only lineup. Both decisions come from a desire to give the customers what they want, and every customer wants the vehicle that's just right for them.

To see the results of our "Gas Or Diesel" readers' poll, go to

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