The Case for Buying a Diesel Truck

There’s a decent amount of science under the hood of vehicles powered by an internal combustion engine, though the carbureted days of Venturi effects and volumetric float measures are mercifully behind us. Gasoline-powered engines mix air and fuel in a cylinder, using a spark to ignite the mixture to move the piston and create power.

Engines fuelled by diesel, however, swap that spark for immense compression, such are the ignition properties of that fuel type. As a bonus, many engineers argue this is an exceedingly efficient combustion method, helping to explain why diesel-powered vehicles tend to stretch their fuel tanks further than a gasoline-powered sibling.

But just how far can it be stretched? Is it possible to drive a hulking truck fuelled by diesel across three provinces, travelling a distance exceeding a Montreal-to-Toronto round trip? We saddled up a new Chevrolet Silverado 1500 pickup equipped with a standard-sized 91-litre fuel tank to find out.

Hitting the road at 8:00 a.m. on a Wednesday meant plunging right into Montreal’s notorious rush hour traffic. Most approaches to the city were under perpetual construction and jammed like a battered office photocopier, with all navigation apps estimating at least an additional hour through the Lafontaine tunnel, during which time we would be sitting still and getting precisely zero miles per gallon. Options like the Cartier and Champlain bridges weren’t much better.

Pointing this Silverado north, we wended up Autoroute 40 out of the city, tracing the far side of the St. Lawrence River until reaching the community of Trois-Riviere, at which point we used the Laviolette Bridge to rejoin the Trans-Canada highway. We kept Super Cruise (GM’s excellent hands-free highway adaptive cruise control system) set to a reasonable 105 km/h, which meant passing some vehicles while others roared by in the outside lane at warp speed.

Here’s some more science for our readers. The amount of energy exerted by a vehicle to maintain forward motion increases nearly exponentially as velocity increases. Smart folk will explain that aerodynamic drag increases with the square of speed; the rest of us can simply imagine the air gets “thicker” the faster a person drives, so shoving a hole through the atmosphere takes more effort and burns substantially more fuel at 120 km/h than at 100 km/h, exacerbated by the towering, blocky nose of a modern half-ton pickup truck.

This — and the law — explains our chosen cruising speed. To make this a fair test that’s useful to our readers, we didn’t engage in any so-called “hypermiling” techniques such as coasting down hills or tucking up behind transport trucks to gain an aerodynamic advantage. Real-world results demand real-world behaviour.

Cruising along the St. Lawrence River, an area of land flatter than this diesel’s torque curve, prompted the Chevy’s onboard computer to estimate fuel economy over the first somewhere south of 6.0 L/100 km, an astonishing achievement made possible by constant cruising at a loafing engine speed of not much more than idle. This holds true for internal combustion engines of all stripes, not just diesels. Of course, that number couldn’t last once the terrain started to undulate, though the indicated average remained near Prius levels of efficiency. At the end of this 1,200-kilometre journey, the trip computer showed an average of just 6.9 L/100 km, a sum confirmed by basic math after the next day’s fill-up.

One oddity that surfaced during our test regarded the Silverado’s readout for an estimated distance-to-empty on fuel remaining in the tank. When we fired it up at the beginning of our journey, the display showed a range of 999 kilometres when brimmed with diesel, a measure we thought was predicated on the driving habits of whoever was last behind the wheel. It took over 300 km of driving for the readout to budge off that figure.

However, after our 1,200-km drive in which we averaged 6.9 L/100 km, the truck still only read 999 kilometres to empty once filled up. This is new, since your author has seen four-figure readouts with his own two eyes in other Duramax-powered models of this truck, most recently when he drove across the entirety of Newfoundland island on one tank in a Sierra 1500 Denali. An accurate distance-to-empty estimate is critical for long-distance highway warriors, and GM should change its lines of code for this calculation back to whatever it was a couple of model years ago.

Like most things in life, better (or at least different) equates to more expensive. In this case, Chevy charges a markedly reasonable $1,195 for the Duramax diesel in this pickup truck, a motor accompanied by an extended warranty good for five years or 160,000 km. If one were hewing to the official fuel economy ratings provided by Natural Resources Canada (NRCan), which suggest the diesel beats the common 5.3L gasser by approximately 4.0 L/100 km in combined driving conditions, it would take only a couple years to make up the initial extra investment given the delta in per litre price currently shown between gasoline and diesel at filling stations near this author’s home. However, as our experience shows, it is startlingly easy to beat the official highway cruising numbers, suggesting the payoff could happen sooner.

Given the numbers belted out by this engine — 305 horsepower and 495 lb-ft of torque, which is more grunt than any other mill currently offered by GM in the Silverado — choosing the Duramax is a no-brainer. If any of yer buddies question the decision, just tell them it’s approved by science.