17 MPG combined. Nobody buys a 2018 GMC Sierra K15 4WD with the 6.2L V8 expecting Prius-like efficiency. This truck is about raw power, towing capacity, and a commanding presence. The fuel economy is simply the price for those who need, or frankly, just want, what this particular Sierra offers.

City and highway performance

The EPA estimates for the 2018 Sierra 6.2L 4WD are 15 MPG in the city and 20 MPG on the highway. The city figure reflects the engine’s tendency to consume fuel more rapidly during stop-and-go driving; the large displacement V8 requires more fuel for each acceleration. The 20 MPG highway rating might seem respectable, but it’s important to maintain a light foot on the accelerator. The eight-speed automatic transmission helps keep the engine at lower RPMs on the highway, but aggressive passing or hauling will drop that number quickly.

Annual fuel cost

According to the EPA, the estimated annual fuel cost for the 2018 GMC Sierra K15 4WD 6.2L is $3,400. This figure is based on driving 15,000 miles per year and using national average fuel prices. Your actual fuel costs will vary depending on your driving habits, the type of driving you do (city versus highway), and local fuel prices. If you primarily use this truck for short trips around town with frequent stops and starts, and if gas prices in your area are above average, expect to spend considerably more than $3,400 annually. If you do mostly highway driving and take advantage of lower fuel costs in certain regions, your cost may be a bit less.

Real-world expectations

While the EPA estimates are a good starting point, real-world fuel economy for the 2018 Sierra 6.2L can differ significantly. If you frequently tow trailers, haul heavy loads, or engage the four-wheel-drive system, expect to see lower MPG numbers than those posted on the window sticker. Aggressive driving habits, such as rapid acceleration and hard braking, also contribute to decreased fuel economy. Many owners find that achieving the EPA-rated gas mileage is uncommon. Check SIERRA MPG across all years.

How it compares

Compared to other full-size trucks in 2018, the Sierra 6.2L 4WD is near the lower end of the fuel economy spectrum. A comparably equipped Ford F-150 with the 3.5L EcoBoost V6 engine achieves around 19 MPG combined. The RAM 1500 with the 5.7L V8 and eTorque mild-hybrid system manages about 17 MPG combined, similar to the Sierra, but with a slight edge. Even GM’s own 5.3L V8 in the Sierra returns about 19 MPG combined. These differences are significant to the budget-minded buyer, but the 6.2L is often chosen by those prioritizing maximum horsepower and torque over fuel savings. For those buyers, compromises made for better efficiency are unwelcome. For all Gmc fuel economy data, check here.

Tips to maximize efficiency

While you can’t fundamentally change the 6.2L engine’s thirst, there are steps you can take to improve fuel efficiency. Maintain a steady speed on the highway and avoid unnecessary acceleration and braking. The Sierra’s instantaneous MPG readout is a helpful tool; use it to learn how your driving habits affect fuel consumption.

Ensure your tires are properly inflated. Underinflated tires increase rolling resistance, which reduces fuel economy. Check your tires regularly and inflate them to the pressure recommended on the door jamb sticker. Be sure to check them when cool for an accurate reading.

Reduce excess weight in the truck bed or cabin. Every extra pound adds to the load the engine must carry, so remove any unnecessary items. Surprisingly, decluttering the average pickup can make a difference.

Plan your routes carefully to avoid stop-and-go traffic. Idling consumes fuel without covering any distance. Using a navigation app to find the most efficient route can save you fuel and time.

Consider using a fuel additive designed to clean fuel injectors. Clogged fuel injectors can reduce engine efficiency. A fuel system cleaner can help restore proper fuel flow and improve fuel economy, especially on a higher mileage vehicle.