Why The 2018 Ford F-150 Diesel 2WD Gets 30 MPG And The 4WD Only Gets 25

Illustration for article titled Why The 2018 Ford F-150 Diesel 2WD Gets 30 MPG And The 4WD Only Gets 25
Photo: Ford
Truck YeahThe trucks are good!

Ford says it has received official EPA fuel economy numbers for the new 2018 Ford F-150 3.0-liter Power Stroke diesel, and the figures are good if you get the 4x2. But if you want power to all four wheels and you’re not a fleet customer, the numbers are much, much lower.

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Hop over to Ford’s press release, and you’ll read that “The 2018 Ford F-150’s first 3.0-liter Power Stroke diesel engine officially boasts EPA-estimated ratings of 30 mpg highway, 22 mpg city and 25 mpg combined,” and that that those EPA numbers are the highest of any full-size truck.

But a Ford representative told me over the phone that those MPG figures—which won’t be on the EPA’s official website until May—only apply to 4x2 models, and the that the four-wheel drive version of this same truck scores an EPA rating of 25 MPG highway, 22 MPG combined and 20 MPG city.

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That’s five MPG lower on the highway just for checking the “4x4" box.

Illustration for article titled Why The 2018 Ford F-150 Diesel 2WD Gets 30 MPG And The 4WD Only Gets 25
Photo: Ford

Looking at other diesel vehicles like the Ram 1500 EcoDiesel, Jeep Grand Cherokee EcoDiesel, Chevrolet Equinox diesel and Chevrolet Colorado diesel for reference—and also looking at gas versions of the F-150—the difference in highway fuel economy between 4x2 and 4x4 versions of the same truck is usually around one and two MPG. I can’t say I’ve ever seen a gap as high as five.

I reached out to Ford to learn more, and a company representative told me that it comes down to how the vehicles are configured. The 4x2 is a SuperCrew with a tall 3.31 fuel economy-oriented final drive ratio and all-season tires on 20-inch wheels. The 4x4 is also a SuperCrew, but it gets all-terrain tires on 20-inch wheels, a towing-oriented 3.55 final drive ratio, and a Torque on Demand transfer case.

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The 4x4's all-terrains likely add rolling resistance, and the shorter final drive ratio likely brings the engine to a less efficient operating point during highway cruising.

The four-wheel drive system, with its added weight, increased drivetrain losses and perhaps more protruding hardware (which could affect aerodynamics) surely also contributes to the lower fuel economy. The Torque on Demand system is automatic, which I suppose could sap a bit more power than a driver-operated system (even though modern full-time four-wheel drive systems are fairly efficient).

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It’s worth mentioning that Ford says its fleet-only XL and XLT 4x4 models—which come with shift-on-the-fly transfer cases—score a decent 28 MPG highway, 24 combined, 21 city. Those trucks, like the retail 4x4s trims, come with all-terrain tires, though unlike the retail trucks they have the taller 3.31 axle ratio.

But if you’re not a fleet customer, the highest fuel economy you’ll get in the 4x4 Ford F-150 3.0-liter Power Stroke diesel is 25 MPG, and if you’re okay with only two-wheel drive, you can buy a truck rated as high as 30 MPG highway.

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I must say I’m surprised that, according to Ford, this delta comes down to just tires, final drive ratio, drivetrain efficiency and weight of that drivetrain. Other automakers offer trucks with the same motors but with different final drive ratios, different tires and different drivetrain options, and yet I’ve never seen such a huge delta in EPA estimated highway fuel economy between variants of the same truck, especially without significant differences in aerodynamic treatments.

A Ford representative told me he’s going to send me a statement on the topic, so hopefully we’ll learn more soon.

Sr. Technical Editor, Jalopnik. Always interested in hearing from auto engineers—email me. Cars: Willys CJ-2A ('48), Jeep J10 ('85), Jeep Cherokee ('79, '91, '92, '00), Jeep Grand Cherokee 5spd ('94).

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DISCUSSION

smazma
Summazooma

“...just tires, final drive ratio, drivetrain efficiency and weight of that drivetrain.”

That’s not a “just” accumulation of factors, especially since you also might have a taller ride height wreaking havoc on aero drag, just as much as all of the factors above wreak havoc on mechanical drag.

That added weight might have pushed the 4x4 into the next-up test weight class, making for a more stringent set of parameters for coast-down (beyond the tires or driveline factors).

Keep in mind, too, that we’re talking about rounding that can sometimes make a difference seem greater than it might in the calculations.
Say, a calculation that lands on 25.4 for 4x4, with the 4x2 landing on 29.5. Real-world difference actually might be less, especially on vehicles that might be more typically equipped than (for example) that 30mpg 4x2 is for label purposes. The actual margin for error, too, can be a few %, so there’s even more of an opportunity for closing that gap in real-world.

This margin is the kind of thing that kills development teams because they all know just how close they were from a different outcome, sometimes influenced not by what would have mattered for fuel efficiency (or, for that matter, sometimes anything that really is significant for marketability).