Photo courtesy Hino Motor Sales USA

For the fifth year in a row, Hino ranks highest in customer satisfaction for medium-duty trucks.

Professionals using Class 5-7 work trucks are finding increased reliability from their engine and fuel systems, according to a new survey from J.D. Power and Associates. However, when breakdowns occur, they are more prolonged than before.

Compared to other diesel emission controls, selective-catalytic reduction technology, which injects urea into the exhaust stream to neutralize tailpipe pollution, is preferred among these truck owners, the study notes. Overall satisfaction ranked at 760 points on a 1,000-point scale. With urea equipment factored in, satisfaction jumps to 778 points.

The survey, released on Oct. 18, canvassed owners of medium-duty truck engines and transmissions for the 2011 model year, which was the first full year that manufacturers sold trucks under the stringent 2010 federal clean-diesel rule. The survey covers both gasoline and diesel engines. J.D. Power, like ENR, is a unit of the McGraw-Hill Cos.

Overall reliability for the category has increased since the last year's survey. Engine and fuel problems fell to 40 problems per 100 trucks this year, down 11 problems per 100 trucks in 2011. But the average length of unscheduled downtime shot up 2.7 days, to 13.4 days. When they break, the new emission controls and other components are more difficult to repair, says J.D. Power.

"As engine manufacturers continue to make advances in technology, there will likely be fewer problems," says Brent Gruber, director of J.D. Power's commercial-vehicle practice. "However, the trade-off is that, when problems occur, they will likely be more complicated and require more downtime to fix." Earlier studies on Class-8 heavy-duty trucks indicate that engine reliability has flagged since the federal 2010 emission rules kicked in.

Hino, a unit of Toyota, took the top prize for overall customer satisfaction, with Cummins and Paccar close behind. Owners of Ford and Navistar trucks reported below-average satisfaction. Hino has won this J.D. Power award five years in a row.

Owners of truck engines in the Class-5 segment reported the best fuel economy and reliability, with 10 miles per gallon and 27.1 PP100, respectively. Fuel economy and reliability decrease as the trucks get larger, the study shows.