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Fuel Management

Pros and Cons of Gas Vs. Diesel in Class 3-4 Trucks

Choosing between gasoline- or diesel-powered trucks requires striking the right balance between performance, fuel efficiency, and budget.

November 2011, Work Truck - Feature

by Staff

Gasoline or diesel: Which engine type works best for Class 3-4 truck applications?

This is an age-old question without a clear-cut winner. Each offers advantages and limitations. The key is determining exactly how the truck will be used and then selecting the engine type that strikes the right balance between performance, fuel efficiency, and budget.

What factors should fleet managers consider when deciding between gasoline and diesel engines in Class 3-4 (10,001- to 16,000-lb. gross vehicle weight rating) trucks? Here are nine points to serve as a guide:

1. Fuel Efficiency

Advantage: Diesel
According to the U.S. Department of Energy, diesel engines offer 30- to 35-percent greater fuel economy than comparable gasoline engines.
"By design, diesel engines operate with a combustion process that's leaner, burning less fuel than a conventional spark ignition (gasoline) engine," explained Roger Gault, technical director, Truck & Engine Manufacturers Association (EMA), a trade association representing worldwide manufacturers of internal combustion engines used in applications such as trucks and buses; farm and construction equipment; locomotives; marine vessels; and lawn, garden, and utility equipment.

Diesel fuel also has higher energy density than gasoline, which means less fuel is required to generate the same power as gas, improving overall fuel economy.

2. Acquisition Cost

Advantage: Gasoline
The diesel engine's fuel efficiency advantage, however, must also be weighed with its bigger price tag. In Class 3-4 trucks, the incremental cost for the diesel engine is between $5,000 to $8,000 or more than its gasoline counterparts. The diesel/gasoline price gap has nearly doubled over the last seven years due to the exhaust after-treatment technologies developed to comply with Environmental Protection Agency (EPA) regulations for diesel emissions (in 2004, 2007, and 2010).

Will the truck be driven a sufficient number of miles per year to recoup the higher up-front cost for the diesel engine with fuel economy savings? A general rule of thumb for a mileage break point is 30,000 annual miles. Above that number, diesel usually makes financial sense. At or below 30,000 miles, gasoline is a viable lower-cost option. Run a fuel-cost/comparison analysis specific to your truck's application to calculate the payback period to assess whether the diesel engine will generate cost savings, within an acceptable timeframe.

3. Fuel Cost Per Gallon

Advantage: Gasoline
"Over the past ten years, diesel has averaged nearly 14 cents more per gallon than unleaded gasoline," said Steve Jansen, truck services account executive, Donlen, a Northbrook, Ill.-based fleet leasing and management company. "At its peak in December of 2008, diesel cost averaged more than 76 cents per gallon more than gasoline. Historically, diesel has been more expensive per gallon as a result of higher taxes and environmental restrictions."

Another benefit of gasoline is availability, according to Michael Macik, a strategic consulting analyst for ARI. "There are certain areas where stations do not necessarily have a diesel pump," he noted. "This could hamper drivers' productivity if they are spending too much time looking for places to fill up."

4. Maintenance Cost

Advantage: Gasoline
"Over time, regular maintenance on a diesel generally will cost more than a gasoline engine," Jansen said. "The diesel engine has components that are either not found on a gasoline engine or require servicing more often. The oil reservoir is larger in a diesel engine and the water separator and fuel filters will require replacement more often. Gasoline engines have longer service intervals for engine oil, spark plugs, and engine coolant."

Gault of EMA agreed: "I think there tends to be greater maintenance with the diesel. Oil capacities tend to be higher. So, if the oil change interval is the same and you have 50 percent more oil in the diesel, then that tends to be more expensive than the gasoline. Also, historically, there has been more maintenance with diesel fuel systems - such as changing filters more frequently."

5. Engine Longevity

Advantage: Diesel
As a frame of reference, according to Brian Tabel, retail marketing manager for Isuzu Commercial Truck of America, the design life of the gasoline engine for Isuzu's NPR cab-forward is 200,000; the diesel engine is B-10 rated for 310,000 miles.

Why are diesel engines expected to last substantially longer than comparable gasoline engines?

"Diesel engines have high-compression ratios and high cylinder pressure and, as a result, require sturdier engine parts - for example, block and cylinder heads, valves, crankshaft, and pistons," said Jansen of Donlen. "This is necessary to dissipate the higher engine temperatures and the higher compression ratios attained in a diesel engine. Also, a diesel engine's exhaust system will outlast a gas engine exhaust system because diesel fuel exhaust is not as corrosive as gasoline engine exhaust."

Gault of EMA pointed to the diesel engine's operating efficiency as another key to its longevity. "The diesel achieves higher torque at much lower speed, so it's operating at much lower rpm [revolutions per minute], a greater percentage of the time than gasoline engines. And the lower engine speed translates into fewer times a piston has to move up and down, the fewer times a valve must close, and so forth. All these things happen lots of times, but not quite as often as it does in a gasoline engine - and that impacts overall life."

6. Trailering

Advantage: Diesel
"The diesel engine is a more suitable choice if towing capacity is critical to your operation," Jansen of Donlen advised. "The torque advantage of diesel engines is better suited for pulling heavy loads up steep grades. The relatively high-compression ratio necessary to ignite the diesel fuel (17:1 diesel versus 9:1 gasoline), allows the diesel engine to generate all its torque and power at a lower rpm."

Macik of ARI agrees. "It's all about using the right tool for the job," he said.  "While appropriate for certain demands, using a gasoline truck for heavy towing in most cases will result in significantly reduced engine life and increased gasoline consumption."

Do the truck's towing requirements necessitate a diesel engine? Or will a gasoline engine work fine? Consult the manufacturer's rep or fleet advisor for max trailer ratings of the vehicle and engine type under consideration.

7. Specialty Body/Equipment Options

Advantage: Depends on upfit requirements
Are there body or equipment considerations with gasoline versus diesel?

"Yes, normally with diesel engines, depending on manufacturer, the DEF [diesel exhaust fluid] tank or exhaust pipe may need to be relocated to accommodate equipment," Jansen answered. "In regards to PTO provision availability, normally a PTO prep option is available with diesel engines only. However in recent years, depending on the manufacturer, PTO provisions are being offered on gasoline engines as well."

If your truck equipment requires a PTO, contact the truck manufacturer's rep to confirm the gas truck availability. This will save time and headaches up front, should the gas engine prove incompatible.

8. Disposition/Resale

Advantage: Diesel
Which is better for resale values? "The market perceives that a diesel-powered truck with 150,000 miles on it has much more remaining useful life than a gasoline-powered truck with comparable miles. And therefore, the diesel commands a higher price," Jansen of Donlen said.

Macik agrees and added that "there's such a variety of companies and industries that legitimately need diesel trucks for towing and increased payload. Many of these companies are smaller, and, consequently, have a smaller fleet budget - they are going to be looking for used vehicles. This means an opportunity to attract a larger buyer base, increased demand, and therefore command higer premiums."

9. Environmental Impact

Advantage: Comparable
What's the difference between gas and diesel in terms of environmental impact? Which produces fewer emissions? "Historically, diesels struggled with that," said Gault of EMA. "They had higher emissions in terms of particulates and NOx (nitrogen oxide). With the latest round of regulations, the differences between gas and diesel are pretty much non-existent. If you're buying the new product that meets the latest emissions standard, I'm not sure there is a differentiating level [in emissions] at all."

Tabel of Isuzu agreed: "Both [gas and diesel emissions] are about the same since the 2010 EPA diesel emissions requirements have been implemented."

Jansen of Donlen pointed to diesel's fuel economy advantage as the equalizer with emissions. "Diesel as a vehicle fuel emits more greenhouse gas emissions when consumed than unleaded gasoline, but its higher energy content per gallon results in higher fuel efficiency," he said. "Therefore, in similarly equipped vehicles, a diesel vehicle can go further on a single gallon of fuel than a similar truck on gasoline. As a result, diesel's greenhouse gas emissions are comparable to those of a gasoline engine due its increased fuel economy."


  1. 1. [email protected] [ July 15, 2013 @ 05:16AM ]

    To change oil in diesel engine cost me around $100 for the same truck gas engine oil change is around $20. That's alone pay off the gas saving. Go gas...

  2. 2. John Milhon [ August 02, 2013 @ 02:39PM ]

    One of the largest considerations that I have regarding the decision on a gas engine versus a diesel engine is will the truck normally be required to pull excessive weights and will it normally be able to achieve a speed above 45mph for at least 40 minutes at least twice a week to allow the vehicle to go through the regeneration process. If I have a service vehicle that tends to idles a lot and will not obtain the 45mph needed for regeneration, I strongly recomend a gas powered truck to avoid interuptions in service while the vehicle is either in de-rate or running through a manually commanded regeneration. The extra time taken to add the DEF fluid in Fleet vehicles, train the operators, and the multiple regeneration problemsthat require the vehicle to be sent to the dealer for warranty repairs are not worth it for a city only service vehicle.

  3. 3. TJ [ August 19, 2013 @ 07:49AM ]

    Running a farm finds gasoline to be less of a cost when it comes to repairs since we can do all of them in-house!

  4. 4. Kyle d [ May 04, 2014 @ 04:14PM ]

    Diesel is what u really need if your moving a lot n loaded. 2 cords of red oak is almost 2 ton. 3 a day 6 days a week. None stop. No problems and when some one rides my ass hoping wood will fall off the truck I drop it in 4th n just fly away. That was 2 n a half years ago. I just started the truck first time today in almost 3 years. Kept it in 4th just flying around the block laughing like a school girl. You will never go wrong with a diesel. Mine is a 97 7.3 turbo f 350 just shy of 400,000 miles. Got it 3 grand when I was 19 in 2007. When it started out with 250,000. I'm about to re do my whole rear end only because the guy I bought it from used to fill it with salt for his farm. He had 5 of the same trucks. IV had guys stop by try to buy it n I tell them stupid high number's. Once u find the right diesel truck life is much easier. Just wanted to tell the world I love my 7.3 turbo!

  5. 5. jr23 [ October 13, 2014 @ 02:04PM ]

    for kyle you have an older truck no def,no exhaust regen and a lot of less controls plus it sounds like a manual trans. the current models have lots of controls. i was surprised to see UPS going back to gas. but the regen might be a problem with door to door del and not much road time.
    heave hauling daily or long distances diesel is king lots of local stops gas .
    the thing i have noticed in the recent time trucks are weighing empty
    what they used to weigh loaded for the same carrying capacity although towing capacity grew but every company does not need towing they need cargo and economy

  6. 6. Dustin Fink [ December 02, 2014 @ 08:00AM ]

    Great information. Im a Junior in High School. I go to BCIT which is a Vocational (Trade) school. My career major is Auto/Diesel. I am ASE certified. Im doing a career major project in my english class and I used this story as one of my sources, because of the great information. Please if you have anymore information on the differences between Diesel and Gas engine email me. Thank you.

  7. 7. Zach W [ February 04, 2015 @ 09:44AM ]

    I like the information given here because I'm 17 and wanting to get myself a truck. I see that gas cost less than diesel when it comes to fixing the vehicle and the fuel. But which one will last longer for you? I want a dependable truck that I can count on and drive around town and take long trips with. Should I go Diesel or Gasoline?

  8. 8. Nick T [ March 10, 2015 @ 06:29AM ]

    Im just putting my opinion out there a diesel is a far better choice if your wanting a truck especially if your looking to lift it. First off they have better fuel efficiency than gas truck. I own a f250 its a 6.0 turbo diesel lifted on 37s and im a younger guy and i honestly would never go back to a gas truck. I drive one of the nicest lifted truck where im located and to have a 8inch lift and 37s once you straight pipe with a bigger exhaust i have a 5inch and bought a programmer and with some custom tunes im getting 15 mpg which is pretty good while running a 145hp tune with economy boosts and feels great being one of the biggest trucks on the road that will beat alot of cars and any other gas truck off the line! And if your 16 or 17 and know your getting a truck look into getting a diesel for the long term, they last longer, resale is higher, there is too many things you can do performance wise, they are faster, better mpg, sound better etc..


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