Diesel HD Trucks Burn Significantly Less Fuel Than Gas Ones in Our Highway Test

• Heavy-duty trucks are exempt from publishing EPA mileage, but in our real-world highway fuel-economy test, we found diesels burn a lot less fuel.
• The diesel trucks averaged 18 mpg, and the gas-fed models averaged 15 mpg, which means the compression-ignition pickups returned 20 percent better fuel economy.
• Still, of the 22 HD pickups we’ve put through our HFE test, only two diesels cracked 20 mpg–a 2018 Ram 2500 and a 2023 Ford F-250 Super Duty.

Welcome to Car and Driver’s Testing Hub, where we zoom in on the test numbers. We’ve been pushing vehicles to their limits since 1956 to provide objective data to bolster our subjective impressions (you can see how we test here).

Since 2016, we’ve tested hundreds of new vehicles on our 75-mph highway fuel-economy route. All of our tests are performed on the same 200-mile out-and-back loop on Michigan’s I-94, which was designed to give us a better idea of how a vehicle performs in the real world. However, certain vehicles aren’t required to publish the typical EPA mileage estimates (i.e. those with a gross vehicle weight rating (GVWR) greater than 8500 pounds). That applies to heavy-duty pickup trucks that are popular with Americans, so we’ve collected all the Ford, GM, and Ram models we’ve tested on our HFE route to compare their real-world results.

Diesel HD Trucks Dominate Our HFE Test

It’s likely no surprise that these big and heavy trucks gulp rather than sip whatever fuel is in their massive tanks. Modern-day HD pickups all have a diverse selection of engines that include everything from Ford’s monstrous gas-fed 7.3-liter V-8 to Chevrolet and GMC’s venerable Duramax diesel 6.6-liter V-8 to Ram’s Cummins diesel 6.7-liter inline-six that offers standard- and high-output versions; Ford’s Power Stroke diesel 6.7-liter V-8 also offers two different outputs.

No matter their displacement, cylinder count, or fuel type, none are exactly parsimonious at the pump. Still, one thing rings true: the diesel trucks we’ve tested burn significantly less fuel at highway speeds, averaging 20 percent better fuel economy than their gas-swilling counterparts. That’s based on averages of 18 mpg for the diesel models and 15 mpg for the gas ones. It’s worth noting that every truck we tested had an automatic transmission and four-wheel drive, but their bed lengths, body styles, tires, and equipment lists varied.

Diesel engines are a popular option among HD trucks thanks to their prodigious torque output and generally better fuel economy versus their gas counterparts. The latter is evident by the results of our HFE test. While 17 of the 22 trucks we tested were fitted with a diesel powertrain, only one gas-fed model—a 2024 Chevy Silverado 2500HD High Country that got 18 mpg—was in the top 10. Still, combined with the other four gassers, which had the four worst HFE results, they averaged 15 mpg.

2024 Ford F250 Super Duty

Of the diesel trucks we’ve tested on our 75-mph real-world route, only two returned 20 mpg—a 2018 Ram 2500 with the S/O Cummins diesel and a 2023 Ford F-250 Super Duty fitted with a High-Output Power Stroke. The rest returned between 16 to 19 mpg. Altogether, the diesel trucks averaged 18 mpg. We’ll point out that we also tested a supersized Ram 2500 AEV Prospector that got 15 mpg. The worst performing diesel, yes, but its aftermarket 40-inch tires make it an orange among a group of OEM apples. So we omitted it from the roundup of 22 trucks.

Zooming out on our results, three trucks returned 14 mpg, one returned 15, five returned 16, four returned 17, three returned 18, four returned 19, and two returned 20. Below are the five best and five worst real-world figures:

5 Best HFE Results

• 2018 Ram 2500 Limited Crew Cab (diesel: 20 mpg)
• 2023 Ford F-250 Super Duty Platinum Tremor Crew Cab (diesel: 20 mpg)
• 2019 Ram 2500 Tradesman Regular Cab (diesel: 19 mpg)
• 2017 Chevy Silverado 2500HD LT Double Cab (diesel: 19 mpg)
• 2020 Chevy Silverado 2500HD High Country Crew Cab (diesel: 19 mpg)

5 Worst HFE Results

• 2020 Ford F-350 Super Duty Platinum Tremor SuperCrew (gas: 14 mpg)
• 2017 Ram 2500 Laramie Crew Cab (gas: 14 mpg)
• 2020 Chevy Silverado 2500HD Custom Crew Cab (gas: 14 mpg)
• 2017 Ford F-250 Super Duty XL SuperCab (gas: 15 mpg)
• 2017 Chevy Silverado 3500HD LT Crew Cab DRW (diesel: 16 mpg)

We don’t point these figures out to attack the segment. After all, these trucks are intended for tough jobs, towing and hauling immensely heavy loads, not hypermiling. Instead, we simply sought to illuminate the real-world mpg differences between the HD pickups we’ve tested as well as highlight the best and worst when it comes to highway duty. After all, the optional diesels often add a lot to the price of a truck. Take the 2017 (gas) and 2018 (diesel) Ram 2500. Running 50,000 miles (unloaded) on the highway represents a 625-gallon savings. You might not recoup the optional cost in a year, but depending on how you use it, the lifetime cost may be close. Now, who has a 10,000-pound trailer they can give us to redo all this testing?