As you may already know, we spent a week behind the wheel of the 2020 GMC Sierra 1500, the new-generation truck that’s built on the GM T1 platform. Our test pickup’s key feature is the turbo-diesel 3.0L I-6 LM2 turbo-diesel Duramax engine. It’s rated at 277 horsepower and 460 pound-feet of torque and mated to the GM 10-speed automatic transmission which transfers power through either the rear wheels or optional 4WD.
One of the main reasons consumers might opt for the Duramax straight six instead of the two available 5.3L V8s (the 5.3L L82 V8 and the 5.3L L84 V8) or the 6.2L L87 V8 is better fuel economy. While diesel fuel tends to be slightly more expensive than gasoline (in North America, anyway), a diesel-powered truck can typically cover longer distances on a full tank. EPA fuel economy ratings for the 2020 GMC Sierra 1500 4WD with the Duramax I-6 are 24 mpg combined, 22 mpg city and 26 highway.
We took our truck out to see how those fuel economy figures stack up in real-world driving conditions. Since our tests were performed in Canada, the instrument cluster displayed fuel economy in L/100 km. However, we will gladly convert this to miles per gallon for you.
Each test was performed during a cool to mild Canadian spring, with temperatures ranging between 32 and 50 degrees Fahrenheit. The truck was unloaded, with only the driver on board, sending power to the rear wheels the entire time.
During our first route, we drove the 2020 GMC Sierra 1500 diesel through the city, with our route comprised of several stop and go situations. The second run was mostly performed during highway driving at a cruising speed of approximately 71 mph (115 km/h). The table below shows the real-world results we achieved during each run.
|Trip||Trip Distance||Average Speed||Recorded Fuel Economy|
|Trip 1 (Urban)||45.8 miles / 73.8 km||43 mph / 69 km/h||20 mpg / 11.9 L/100 km|
|Trip 2 (Highway)||66 miles / 106.3 km||68 mph / 110 km/h||25 mpg / 9.4 L/100 km|
Although we weren’t able to match GM’s official fuel economy numbers, these results are not that far off, and the cold(ish) weather in which we performed this test is yet another variable.
It’s also worth noting that, outside of actual fuel costs, another expense should be taken into account when figuring total cost of ownership is Diesel Exhaust Fluid, which the GM Duramax LM2 engine requires. Though a tank of DEF should last for several thousand miles, the amount used depends on the driving style, towing, loaded vehicle weight, weather and various other factors.
In addition, depending on the chosen 2020 GMC Sierra 1500 trim level, the turbo-diesel six costs between $2,495 and $4,980 more than the 5.3L L84 V8 with Dynamic Fuel Management, which boasts city/highway/combined fuel economy numbers of 16/22/19 mpg for 4WD models.