WESTLAKE VILLAGE, Calif. -- Fuel mileage differences among medium-duty trucks could mean savings of more than $2,000 per truck per year, according to the J.D. Power and Associates.

Its 2010 U.S. Medium-Duty Truck Engine and Transmission Customer Satisfaction Study found that the cost difference between medium-duty truck engines with the highest fuel mileage and those with the lowest can be as high as 18 percent.

A small fleet of 17 trucks, then, can save up to $36,000 a year on average depending on the model.

Engines with the highest reported mileage average 9.3 mpg, compared to the industry average of 8.4 mpg.

better fuel-efficient trucks typically score 50 points higher in overall engine satisfaction, the study noted.

"Although some fleet owners may be tempted to purchase gas engines given that gas prices are currently much lower than diesel, a more fuel-efficient diesel engine will ultimately lead to much lower annual fuel costs," said Todd Markusic, senior director of the commercial vehicle practice.

Meanwhile, Hino Trucks engines rank highest in customer satisfaction for a third consecutive year, says J.D. Power. They rated particularly well in engine reliability and dependability, average fuel economy and accessibility to components for service/maintenance. Paccar and General Motors follow Hino in the rankings.

The study also found that 10 percent of customers indicate experiencing a fuel problem. On average, satisfaction among these customers is 134 points lower.

The study is based on responses from 1,255 primary maintainers of one-year-old conventional cab medium-duty trucks.