A decade ago, the choice between gasoline and diesel engines in most Class 3 to 7 truck applications was a no-brainer – diesel, of course. At that time there were few gasoline engine options available in heavier trucks and diesel held a significant advantage in terms of fuel efficiency, low-end torque and longevity, for only $3,000 to $4,000 more up front.
Today, however, the decision is a bit more complex. New gasoline engine technology has begun to narrow the fuel-economy and performance gap with diesel. And after progressively stringent federal emissions standards for diesel engines were put into effect in 2004, 2007 and 2010, requiring expensive exhaust reduction technologies, the price gap has essentially doubled, with diesel engines costing about $7,000 to $10,000 more than a comparable gas-burner, causing utility fleet managers to take a hard, second look at gas, when it’s available.
So, in instances where both gas and diesel are available in a particular class truck, which is better for utility and telecom fleets? Utility Fleet Professional spoke with experts at GE Capital Fleet Services (www.gefleet.com) and Donlen (www.donlen.com) to get their take. Here are the criteria they recommend when deciding between gas versus diesel.
When Diesel is Better
Despite the substantially higher price tag, when does diesel make the most sense from a performance and life-cycle cost perspective?
“When the fleet expects the truck to run longer periods of idling time powering auxiliary equipment, they tend to lean towards diesel,” said Ken Gillies, manager of truck ordering and engineering at GE Capital Fleet Services, a leading full-service fleet management company based in Eden Prairie, Minn. “Also when there's heavy towing necessary, they’ll choose diesel because of the engine’s higher torque output.”
Steve Jansen, manager, fleet services and regulatory compliance at Donlen, a full-service fleet management company based in Northbrook, Ill., and wholly owned subsidiary of The Hertz Corp. (NYSE: HTZ), agreed. “If you're taking a [Ford] F-550, and you're putting on some sort of small crane or bucket truck or you're going to do some high-wire stuff, you're probably not even going to think about gas. You'll jump into diesel because it’s going to give you the torque you're going to need and the longer life,” Jansen explained. “The torque is important to get you up and down the road with the weight you're pulling. And if you're taking the truck off-road into brush or something like that, you’re going to need a lot of low-end torque of the diesel to help drive the truck out of those situations.”
What’s the difference in life expectancy between diesel and gasoline engines?
“I'm still a firm believer that gas engines are built to go 200,000 miles. Diesel life is in the 300,000 to 350,000 to almost 400,000 miles range, depending on the size truck and application,” Jansen said.
According to Gillies, another factor that drives diesel selection is fuel economy. “Although the gasoline world has done a great job with efficiencies for fuel injection and various controls, diesel still holds a miles per gallon advantage, which we see as a way to help fleets control fuel costs in high-mileage, high-idle situations,” Gillies said.
What exactly is diesel’s fuel economy advantage?
“The diesel is 15 to 20 percent more fuel efficient than gas,” Jansen said. “And even though the gasoline engines have improved, the one thing that remains the same is that the diesel fuel itself is still 30 to 35 percent more efficient than gasoline [in terms of energy density]. So, theoretically, for every gallon of diesel fuel you put in, you're having to put in 1.3 gallons of gasoline because of the efficiency ratio.”
Gillies estimated the diesel advantage at about 2 mpg, but said that at that rate, “it still takes a long time to clear the higher [initial] cost of the diesel engine, depending on the specifics of the application and the actual road mileage the vehicle is encountering.”
When Gas is Better
In what utility fleet applications is gasoline a good fit?
“A gas engine is suitable in a light utilization vehicle,” Gillies said. “By that I mean light-duty Class 2 to 3 and, in some cases, Class 4, when it’s operating with relatively short idle time. The diesel starts to make more sense if the application requires longer idle time [to operate cranes, buckets and other specialty equipment], even if it's a lighter-class truck.”
Also, if the fleet is considering converting vehicles to gaseous alternative fuels such as CNG or propane autogas, a gasoline engine would be the most economical option because it’s inherently more “gaseous-fuel ready” than diesel, according to Gillies. “It’s about a $9,000 or so conversion cost to equip a gasoline-powered Class 6 truck for CNG. If you take the same truck, spec’d with a diesel engine, and you want to convert it to gaseous fuel, you’re looking at, on average, three times the cost,” Gillies said.
The Bottom Line
Jansen summed up the gas versus diesel deliberation this way: “The whole decision is based on what the job is you're going to call on that truck to do. If it's running from job site to job site to check on workers or as an estimator, carrying a small amount of tools or equipment going out to inspect well sites, then gas is going to be fine. The heavier the job, that's where diesel is really going to pay off, giving you the long life and low-end torque and start-ability you need to drive that truck out of a ditch, whereas the gas [engine] is going to struggle a little bit in that scenario.”
About the Author: Sean M. Lyden is a nationally recognized journalist and feature writer for a wide range of automotive and trucking trade publications, covering fleet management strategies, light- and medium-duty trucks, truck bodies and equipment, and green fuel technologies. He blogs at Lyden Fleet Strategies (www.lydenfleetstrategies.blogspot.com).