Dueling Fuels - RV Enthusiast Magazine

Dueling Fuels

by | Aug 20, 2021 | Education, Performance, Trucks/Tow Vehicles

Diesel or gas? The decision isn’t as clear cut as it once was. We talk to the experts to get their take on the subject — and offer our own experiences to help you make the right decision.
Deciding on a diesel or a gas engine for your towing needs used to be easy. If you were just doing some light towing and wanted something you could use as a second vehicle, a gas-powered truck or SUV was the obvious choice. Flipside, if you planned to tow a large fifth wheel frequently or full-time, a diesel’s longevity and massive torque was the logical decision.

But technology has changed radically in the last few years. There are now small six-cylinder diesel engines in half-ton trucks that rival the performance — and surpass the fuel economy — of their gasoline counterparts. And there are new gasoline V8’s available in 3/4- and 1-ton trucks that can tow nearly as much as a diesel option — and cost around $10,000 less. Diesel engines do tend to last longer, but it’s not uncommon today to get 150,000 or 200,000 miles out of a well-maintained gasoline engine, which begs the question: Is the added cost of a diesel engine worthwhile today?

Cost Analysis

When considering a diesel, cost is always the primary consideration. Diesels have always commanded a higher price tag, owing not only to the heavier-duty components of the engine itself but all the ancillary items that go along with it. However, ever-stringent emissions-control regulations have driven costs even higher.

In the year 2000, the United States Environmental Protection Agency (EPA) adopted new guidelines designed to reduce emissions from on-road heavy-duty trucks and buses by up to 95% and cut allowable levels of sulfur in diesel fuel by 97%. Beginning with the 2007 model year, 100% of on-road diesel trucks required the use of a diesel particulate filter, and by the 2010 model year, 100% also required NOx exhaust control technology. As a result, today’s trucks are equipped with a complex Selective Catalytic Reduction (SCR) exhaust after-treatment system that requires a continuous diet of Diesel Exhaust Fluid (DEF, a solution of 32.5% urea and 67.5% de-ionized water) to break down NOx emissions into harmless nitrogen and water.

Duramax diesel engine
The torque- and fuel-economy gap between gas and diesel engines has narrowed in recent years, making the choice of truck powerplants a lot tougher for RVers.
While the required emissions equipment certainly drove costs higher, the design and intended use of a diesel engine brings extra costs of its own. “Higher-pressure pumps and material cost increases all play a role (in overall cost)” said Rod Romain, chief engineer for Ram trucks. “And with greater capabilities come larger transmissions, frames, brakes and drivelines with higher capacities.” For example, Romain noted that the 1988 Ram truck with the Cummins diesel option had 400 lb-ft of torque; the current Cummins High Output (HO) option produces 1,075 lb-ft of torque.

“Due to their additional emissions-related components, diesels tend to cost more upfront, yes,” said Kendall Fulton, General Motors global chief engineer, diesel engines. “But depending on a customer’s usage and needs, diesels may be a more cost-effective option due over time, thanks to their superior fuel efficiency and durability. Customers that plan on driving a lot of miles, especially while towing, will see long-term cost savings at the pump while enjoying that stellar low-end torque.”

the rpm dial
putting gas in a tank
Late-model Ram pickups (2020 Ram 1500 shown here) incorporate a gauge in the instrument cluster to monitor DEF level. The fluid is added to a special reservoir accessed behind the fuel filler door on the pickup.
Then there are other considerations that diesel ownership brings. Scheduled maintenance will be costlier, as the 6.7-liter Cummins holds 12 quarts of oil while the 5.7-liter and 6.4-liter Hemi gas engines take seven quarts. The 6.7-liter Power Stroke diesel, meanwhile, requires 13 quarts, while the larger 6.2-liter and 7.3-liter gas V8 engines use seven and eight quarts, respectively. There may also be added costs associated with fuel filters/water separators, and during the last several years diesel fuel has been marginally more expensive than gas.

Considering that heavy-duty trucks are not required to post fuel economy ratings, comparing mileage figures against an available gas engine isn’t so cut and dry.

“It depends on customer usage, so each customer would need to calculate their fuel economy in addition to the DEF usage and oil-change cost and frequency,” said Peter Lyon, manager of diesel propulsion systems calibration for Ford Motor Company. “Our fleet customers track cost of ownership closely and can make a precise decision of powertrain selection based on very accurate expected overall costs — and very often select diesel engines based on their usage profiles,” he said.

“Always consider your use and length of ownership,” added Romain. “In some cases, the weight you haul will require a Ram 2500 or 3500 HD with Cummins 6.7-liter. If not, the 6.4-Hemi is a great option and reduces upfront costs. Each owner has a different need and it’s up to them to crunch numbers.” To wit: A Ram 2500 4×2 Crew Cab Tradesman with the 6.4-liter Hemi gas engine can tow up to 17,190 pounds, while the same truck with the standard output 6.7-liter Cummins tows 19,290 pounds — a difference of 2,100 pounds. So, in the case of a trailer that weighs between 10,000-15,000 pounds, for example, it may not make sense to spend the extra money on a diesel — at least from a budgetary standpoint.

7.3-gas-V8: Ford finally replaced the aging 6.8-liter V-10 in the 2020 model year with a 7.3-liter V-8 generating a best-in-class 430 hp and 475 lb-ft of torque, for a tow rating of up to 21,000 pounds.
a Cummins engine
The addition of a Cummins engine to a Dodge truck in 1988 arguably started the diesel horsepower race. Today, the High Output version of the engine is capable of 420 hp and 1,075 lb-ft of torque.
Ram’s 6.4-liter Hemi engine
Ram’s 6.4-liter Hemi engine is a viable option to diesel in a 2500/3500 model truck. With 410 hp at 5,600 rpm and 429 lb-ft of torque at 4,000 rpm, it can tow up to 17,190 pounds.
6.6-liter Duramax diesel
For the 2020 model year, GM offered the 6.6-liter Duramax diesel with an all-new Allison 10-speed automatic transmission that bestowed 3500 series trucks with a towing capability of up to 35,500 pounds — a 52% increase over previous years.
Indeed, while a gas engine may have similar tow ratings to a diesel in a given truck, there’s little doubt that the diesel will be able to pull your load with far less effort. “Both gas and diesel engines are designed to the extreme customer operating targets,” noted Fulton. “However, since the diesel engine is designed to produce greater torque at a lower RPM (engine revolutions per minute), the engine does not operate at the same engine speeds to achieve the same performance. In typical gas engines, the engine must operate at higher RPM to achieve peak torque, meaning gas engines tend to work harder to achieve the same performance. This ultimately equates to durability and longevity to diesel customers when making an engine choice.”

Convenience may be another vote for diesel power. RV Enthusiast staffers who own a diesel truck note that taking on fuel while towing a large fifth wheel is much easier in a diesel truck than with a gas truck simply because of the way most fuel stations are laid out. Truck stops are designed for 18-wheelers, so they’re large and make it easy to pull up to the pump. By contrast, gas pumps are typically designed for passenger cars, so the pumps are closer together and the islands smaller, making it difficult to maneuver to an available pump with a trailer in tow. If you’ve been to a crowded gas station/convenience store/fast food mega center on a holiday weekend, you’ve probably witnessed the struggle for yourself.

Half-Ton Diesels

The addition of a diesel engine option in the half-ton pickup truck segment adds a new wrinkle to the diesel vs. gas debate. For years, many of us wondered why no manufacturer had ever put a diesel engine in a half-ton truck — but by the time these engines were available, more powerful and fuel-efficient gasoline engines seemed to make them a moot point. Diesel engine options in half-ton trucks don’t make as much horsepower as their gas counterparts, cost more and tow less. In fact, Ford recently announced that it would no longer be offering its 3.0-liter Power Stroke V-6 option after July 16, citing slow sales compared to its wildly popular EcoBoost V-6 engine. And yet, Ram continues to hang onto its EcoDiesel option and GM introduced its 3.0-liter Duramax in its half-ton trucks just more than a year ago — then doubled down by offering it in full size SUVs like the Suburban and Tahoe a few months later.

So, does a small diesel still make sense, or not?

For certain customers, it does. Ford elected to drop the 3.0-liter Power Stroke because, with the introduction its PowerBoost hybrid a few months ago (which gets better mileage and has more torque and horsepower than the 3.0-liter Power Stroke), there was really no reason to keep it as an option. But for Ram and GM customers, a small diesel bridges the gap between normally-aspirated V-6 and V-8 engine options — and the additional milage a diesel offers makes sense if the truck/SUV in question will be used as a second family vehicle or daily driver between camping trips.

Ford’s 3.5-liter EcoBoost engine
Ford’s 3.5-liter EcoBoost engine has become a dominant force in the half-ton truck segment, with 400 hp and 500 lb-ft of torque and a maximum tow rating of 14,000 pounds.
3.0-liter Duramax diesel
GM introduced the fuel-efficient 3.0-liter Duramax diesel in its half-ton pick-up line late in the 2019 model year. It is now available in the Tahoe/Yukon and Suburban/Yukon XL full-size SUVs.
Technologies are changing to improve the overall performance and driving experience of the (diesel) engine
Kendall Fulton
“Technologies are changing to improve the overall performance and driving experience of the (diesel) engine,” said Fulton. “For example, we have improved the combustion system of the new 3.0-liter Duramax (by changing the fuel system and piston) to not only increase power and lower emissions but also to ensure the engine achieves incredible fuel economy. Now a customer that previously bought a gas engine can own a 3.0-liter Duramax and, in most cases while driving, not even know that a diesel is under hood. All this technology ensures the vehicle is quiet, fun-to-drive, achieves incredible fuel economy and meets the current diesel regulations. The (added) cost of the engine covers the total package for the customer.”

To put that into perspective, consider: a current model Chevy Silverado 2WD with the 3.0-liter Duramax achieves an EPA-estimated 23 mpg city/33 mpg highway and 27 mpg combined. Compare that to the same truck with the popular 5.3-liter V8 engine, which gets 17 mpg city, 23 highway, and 19 combined. That’s a big difference in fuel economy. The 3.0-liter Duramax isn’t available until you arrive at the mid-grade LT trim level, so if you compare apples-to-apples at the same trim grade, the Duramax costs around $1,000 extra. With an EPA-estimated annual fuel cost of $1,850 for the Duramax compared to $2,450 for the 5.3-liter V-8, you can see that the diesel option will pay for itself in a little more than a year.

Towing capabilities for the two engines are comparable: The Duramax in the same 2WD truck will tow up to 9,500 pounds compared to the 9,700 pounds with the 5.3 (without a towing package).

MB Sturgis Sturgi-Stay T fitting
The 3.0-liter EcoDiesel makes a powerful case for a diesel option in a light-duty truck, with a tow rating of up to 12,560 pounds and an EPA-estimated fuel economy rating of 23 mpg city and 33 mpg highway.
Ram’s 3.0-liter EcoDiesel also offers a viable alternative to gas. The EcoDiesel pulls down an EPA-estimated 23 mpg city/33 mpg highway/26 mpg combined, compared to the popular 5.7-liter Hemi V8’s 17 city/23 highway and 19 combined. Annual fuel costs are estimated at $1,900 for the EcoDiesel, $2,800 for the Hemi. In the same Tradesman trim and Quad Cab 2WD configuration, the EcoDiesel costs $2,700 more as of this writing, but the EcoDiesel gives up very little in the way of maximum tow capacity compared to the Hemi: 12,560 vs 12,750 pounds, respectively.

In summary, there are no longer clear-cut lines when it comes to gas and diesel choices. Newer gas engines offer some capable, economical choices in heavy-duty trucks while a diesel offers greater fuel economy and impressive towing capacity for half-ton customers. It all comes down to crunching the numbers for the truck model(s) you’re considering, intended use and budget — you really can’t make a bad choice.

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