Can the Mammoth GMC Yukon Denali Get Good MPG With a Diesel Engine?

GM used to offer diesel engines in its big SUVs nearly 40 years ago, and it once again has found the diesel religion, making its turbo-diesel 3.0-liter Duramax six-cylinder engine available not only in the latest Chevrolet and GMC half-ton pickup trucks, but also in the mechanically related 2021 Chevrolet Tahoe/Suburban and GMC Yukon/Yukon XL full-size SUVs. Diesels are often reknowned for their stump-pulling torque and sometimes for their fuel-sipping frugality. We wanted to see which of these attributes best applies to the motor in the heavy, luxury-laden 2021 GMC Yukon Denali, so we took it for a fuel economy test to see what  an oil-burner compression-ignition engine in the big beast means for fuel economy.

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The Ride

Redesigned for the 2021 model year, the GMC Yukon rides on a new chassis with a new independent rear suspension; it has new sheet metal inside and out, and a more spacious, more comfortable interior. In its top Denali trim, the Yukon cabin looks absolutely dynamite. Our experiences with the latest Yukon Denali have made us question whether paying even more for a mechanically identical Cadillac Escalade is worth the price, it’s that good. One new powertrain option for the Yukon this year is a turbocharged 3.0-liter diesel engine, an inline six-cylinder engine that GMC labels a Duramax like its big V-8 diesels in the heavy-duty truck line. It pumps out 277 horsepower with a hefty 460 pounds-feet of torque, and it’s mated to a smooth-shifting 10-speed automatic transmission and four-wheel drive. 

The EPA rates this engine combo at 21/27/23 mpg city/highway/combined for a two-wheel-drive Yukon and 20/26/22 mpg with 4WD, which I tested. It can also be had in the long-wheelbase Yukon XL where it is rated to get the same fuel economy despite the SUV’s extra weight. It should be noted that this is significantly better than the 16/20/18 mpg that the standard 5.3-liter V-8 4WD model is rated, or the 14/19/16 mpg of the Denali’s optional 6.2-liter V-8 with 4WD. Four mpg better than the base engine in the combined 4WD rating and 6 mpg better than the optional big V-8 is extraordinary. Pick the big 6.2-liter V-8 and you get more horsepower (420), but the torque is identical to the diesel engine. So if you get all the torque of the big V-8, better fuel economy and it costs less … well, why wouldn’t you go for that engine? 

The Route

I use a fuel economy loop through southeast Michigan that encompases a combination of one-third suburban low-speed stop-and-go and two-thirds constant, mostly flat highway travel. I actually performed the test twice: the first time on a 60-degree day that was experiencing up to 45-mph wind gusts, which caused me to abort the test due to horribly skewed results trying to maintain 75 mph into a 45-mph-plus headwind for half the test. The second test was much better — no wind to speak of, warm temps and calm skies. As is standard procedure for Cars.com fuel-economy tests, my 200-mile loop was performed with tires at the manufacturer’s recommended pressure, windows up and climate control with air conditioning activated. Speeds are kept to within 5 mph of posted speed limits, and driving style is calm and controlled — no stoplight drag races and no slamming on the brakes unless necessary. Calm and consistent is key in these tests. 

The Results

The diesel Yukon Denali 4WD is rated to get 22 mpg combined in the EPA’s test, which is an excellent figure for a vehicle that weighs north of 5,800 pounds in four-wheel-drive guise. Imagine my surprise when the trip computer routinely showed me getting better than 30 mpg in steady-state highway cruising, and with a final tally of 27.9 mpg over 206.1 miles. At the pump, the Yukon swallowed 7.67 gallons of diesel for a calculated fuel economy rating of 26.9 mpg, or nearly 5 mpg better on my route than it’s rated to achieve. And this without taking any extraordinary steps to try and boost mileage. 

That result just makes the diesel seem even more appealing to me. Often, diesels are an expensive optional engine, but the Denali’s diesel engine is actually $1,500 less expensive than the 6.2-liter V-8. To offer the Duramax 3.0-liter for less money than the Denali’s gas engine? That’s astonishing.

There are one or two trade-offs for speccing the diesel for your luxury SUV. It doesn’t have the quiet, refined rumble of the big 6.2-liter V-8 — especially on idle or hard acceleration — and you’ll definitely know you’re driving a diesel because there’s no disguising that noise. But it’s not unpleasant, and it even kind of fits well with the big-rig aesthetic of driving a traditional, enormous body-on-frame SUV. And the engine itself is a gem with massive torque able to propel the Yukon Denali with alacrity. The other trade-off usually comes at the pump: Diesel is usually more expensive than regular gasoline. At the time of this writing, diesel fuel was about 8.4% more expensive than regular gasoline on average in the U.S., but the 6.2-liter recommends premium fuel for optimal fuel economy and acceleration, which is currently more expensive than diesel. So with the initially lower cost of the engine saving $1,500, plus an observed fuel economy result that’s nearly 65% better than the big 6.2-liter V-8’s rating, the math checks out — GMC’s Duramax diesel in the Yukon Denali is a smart choice. 

Related Video: 2021 GMC Yukon Denali: Review

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