Small diesels are all but out of the picture in North America now, consigned to history by a combination of factors including high cost, low fuel prices, Dieselgate, the sale of GM Europe and the rapid rise of electrification. GM’s 1.6 ‘Whisper Diesel’ was short-lived in the Cruze and small SUVs, but there are high hopes for the 3-liter Duramax inline-six in the latest generation of full-size SUVs: Chevrolet Tahoe and Suburban, and GMC Yukon.
This all-aluminum turbodiesel has already found favor in the Silverado full-size pickup and features a DEF emissions aftertreatment system developed at GM’s Canadian Technical Center. Fuel economy by itself is not always a selling point in North American markets, so GM is quick to highlight that the reduced consumption – about 30% over the standard 5.3-liter gasoline V8 in highway driving – comes without compromising durability or capability. Towing capacity is only marginally reduced over the 5.3 and an exhaust brake is available in tow-haul mode, designed to offer more confidence in particular when towing downhill. Peak torque is a mighty 623Nm, the same as for the optional 6.2-liter gas V8.
ETi spent a week with a Duramax Tahoe to see whether it lived up to its billing as the most fuel-efficient SUV in its class. Without towing or much of a load on board, we got 33mpg (8.5L/100km) on the highway and 22mpg (12.6L/100km) around town, which is almost bang on the official figures.
The 281ps-diesel’s smooth power delivery and well-matched, 10-speed transmission is appreciated, although the push-button shifter high on the dash never felt intuitive. The rotary dial favored by Stellantis and now Ford seems like the way to go. Under hard acceleration, the gears shift quickly to keep the engine in the sweet spot below 3,000rpm. The stop-start function works seamlessly.
GM has taken advantage of the inherent balance of an inline-six to create a motor with good refinement and a quiet idle, assisted by a new front cover that reduces noise compared with the Silverado version. There’s a diesel hum in the cruise, but not in an intrusive way. Under load, the sound is pleasantly metallic rather than rattly. The Tahoe pulls strongly from around 1,500rpm, which makes good on the claim of peak torque being available from this speed.
Overall, the Duramax is a great fit for these body-on-frame SUVs, where high torque and substantially lower consumption are perhaps an easier sell than in a smaller vehicle. GM executives believe that diesel’s share of its large SUVs will ultimately lie at 10-15%. The ETi team just hopes that sales reward the company’s faith in diesel and an engineering job well done.
