Ramble On – Diesels Have Gotten Really Good, Guys
Over the holidays, Editor Jason Gonderman threw the keys of our 2018 Pickup Truck of the Year–award-winning, long-term ’18 GMC Sierra Denali HD on my desk and told me to go rack up some miles. (Well, more accurately, I begged and pleaded for the keys because I had a long trip ahead and wanted to do it in something comfortable, rather than some depressing rental car that was probably built in the former Yugoslavia.)
However the trip started, it ended with me feeling a great deal of respect toward our long-term Denali HD and its Duramax L5P V-8 engine. You see, my holiday trip entailed a 4,000-mile journey to and from North Dakota with a brother and his three kids in tow, and our route took us through some of the most inhospitable climates North America has to offer. Driving through Idaho and Montana on the outbound trip and South Dakota and Wyoming on the return, we frequently encountered blowing snow, daytime highs below zero, and gusty crosswinds that could have spelled disaster for lesser vehicles—or for older diesels.
And yet, the Denali faithfully started up after each stop on the journey—as well as every day for the week we were in North Dakota—without a moment’s hesitation. That’s a testament to how impressive modern diesels have become, because even after sitting overnight in single-digit temperatures or less, the GMC cranked over and fired up with total ease. Modern fuel technology deserves some of the credit, as winterized diesel is much more resistant to gelling, but there’s still no denying how impressed my family and I were at how readily the big Duramax jumped to life.
What’s more, aside from a reassuringly muscular full-throttle clatter, the new L5P engine is smooth and quiet in almost every driving situation. On start-up, the engine has a hushed idle not unlike a direct-injected gasoline V-8. One passenger, a friend visiting from Europe who himself drives a small-displacement diesel BMW, was surprised the Denali had an oil-burner under the hood since it doesn’t shake as much as his car does. And merging situations are met with a nice shove in the lower back until you’ve reached traffic speed. Diesel enthusiasts have known this for years, but the Sierra Denali HD runs like a freight train, smooth and determined.
Of course, modern diesel does come with its own drawbacks. Tightening emissions—a targeted consequence of irresponsible coal-rolling—mean modern diesels feature particulate filters that must go through regeneration cycles. When in the midst of those cycles, which typically last a few minutes or so and occur every few hundred miles, the engine gets noticeably worse fuel economy and suffers from a slight loss in responsiveness. Furthermore, we had to refill the diesel exhaust fluid tank once on our trip, lest we put the engine in emissions-reducing limp mode that limits speed to as low as 5 mph until the tank is refreshed. These minor annoyances are worth it when considering the reduced particulate and harmful gas emissions they provide, but the time spent in regen or at the fuel station refilling DEF is nevertheless an inconvenience.
Even so, the Sierra HD and its husky diesel engine got my family and me safely through the frozen mountains and prairies between here and there without needing to plug in the engine block heater or with lengthy warm-up times, and I am duly impressed. It’s remarkable how smooth, driveable, and idiot-proof a modern diesel is. Well done, Denali.