How to Make the Right Choice: Gas vs. Diesel for Medium-Duty Trucks

Weighing whether to select gasoline versus diesel power for work trucks is enough to make your head spin into another dimension – of choice, that is. Thanks to advances in engine designs and greater availability of gasoline power, there is more than ever to think about when picking a gasoline or diesel option, including deciding whether having some of each is the best choice for your truck applications.

So, what to pick? As with most truck equipment questions, “It depends on your operation” is the usual answer. Fair enough, but to fit the engine to the job, you need yardsticks for comparison. Most experts start by pointing out the key operational aspects of each fuel type.

On one hand, diesel engines compared to gasoline engines pump out significantly more torque, provide greater towing capacity, operate more fuel efficiently and, with proper maintenance, deliver significantly longer life.

On the other hand, gasoline engines outshine diesel in their horsepower and acceleration performance, especially on hills; may have lower maintenance costs because parts are easier to locate; and are the easiest to fuel up as not all service stations carry diesel fuel.

Fuel cost alone is a big consideration, too, given that diesel fuel is now more expensive than gasoline in most locales. And then there’s the matter of diesel technology developments, many of which are driven by emission regulations.

Evolving Technology
Current tech includes variable geometry turbochargers, diesel exhaust fluid and particulate filter aftertreatment exhaust systems. To be sure, today’s EPA-compliant diesels are not simple, yet they are engineered to be quieter and more powerful.

Of course, gasoline power has been evolving, too, especially to deliver higher power performance. That’s a major selling point for OEMs that have jumped back into the gasoline pool. The same goes for the Big Three, which have never strayed from having gas on the menu. Ford, General Motors and Ram offer both diesel and gasoline power plants in their heaviest medium-duty trucks, such as Ford Super Duty and Chevy Silverado/GMC Sierra HD models.

“Although your fuel choice will largely depend on your application requirements, there are many factors when comparing the two, including longevity, service/maintenance, towing, total cost of ownership, and more,” Joe Birren, fleet operations manager of truck and upfit engineering for Merchants Fleet, a provider of fleet management solutions, pointed out in a blog post (see www.merchantsfleet.com/industry-insights/diesel-vs-gas-trucks/).

Total Cost of Ownership
In Birren’s view, while diesel trucks have a higher initial acquisition cost, you should also consider the total cost of ownership to operate them, including fuel spend over time, preventive maintenance costs, depreciation impact, and other financial costs over the truck’s expected or planned life cycle.

“Diesel engines, when properly maintained, typically have a longer service life compared to their gasoline counterpart,” he noted. “Advances in metallurgy, fuel, and engine management technology have greatly improved durability over the last decade.

“One key consideration is the service, maintenance, and warranty perspective regardless of OEM or truck class,” Birren continued. “Do you have a local repair facility or dealership with trained, certified technicians who can handle late model diesel engine repairs and maintenance? Will you need to travel further out to a dealership if warranty issues arise and your regular service center is unable to handle your service needs?”

As to factoring an mpg benefit, he advised that 30,000 to 35,000 annual miles is a good baseline to realizing the fuel economy advantages of a diesel. “However, this depends on your application, such as the average payload weight, aftermarket body or equipment requirements, towing, and operating conditions.” Birren added that when it comes to payload capacity, gasoline holds the advantage. He noted that a diesel engine could add approximately 800 pounds over a gas engine on the same chassis model.

Too Little or Too Much
Then there’s the crucial matter of going with too little or too much, as laid out in a blog post by specialized body builder Knapheide (see www.knapheide.com/blog/gas-vs-diesel-which-to-spec/). “While the vast engine choices create additional value, it can also create a dilemma when it comes to properly spec’ing the engine for the intended application of the vehicle. … Over spec’ing and under spec’ing are common mistakes, leading to lost efficiency, productivity or a longer return on investment period.”

With truck makers widening engine choices lately, including bringing gasoline back to several model lineups, the company pointed out that “while gasoline engines still dominate Class 1 and diesel engines make up the majority of Class 6 and Class 7, these new engine choices make the decision much more analytical than ever before.”

Given this, key selection considerations should include higher acquisition costs for diesel, which Knapheide said can stretch “from $8,000 more in light duty commercial vehicles up to $12,000 in heavy duty commercial trucks.”

Another top factor should be power-takeoff units, where needed. “To avoid potential compatibility issues, ensure the engine (and transmission) you select will allow for PTO installation,” the company advised. “At one time, your only choice for PTO compatible engines were diesels. Today, many manufacturers offer gas engines that can easily accommodate a PTO unit for auxiliary equipment.” Also keep in mind that “diesel engines idle at a lower speed and are engineered for severe duty cycles, making them the more popular choice within high-idle applications.”

Clearly, despite the ramp-up in gasoline engines, medium-duty diesel isn’t going anywhere. But just how hot is gasoline in medium-duty? Here’s one solid yardstick: Isuzu Commercial Truck of America recently reported that its gasoline-powered N-Series truck has made significant inroads since it was rolled out fewer than five years ago. Backing that up, in June the OEM stated it had produced its 100,000th such model for the U.S. and Canadian work truck markets.

About the Author: David Cullen is an award-winning journalist who specializes in covering the trucking industry. Based in Connecticut, he writes for several business publications.