24 MPG combined might not sound impressive, but consider what the 2021 GMC Sierra 4WD with the 3.0L Duramax diesel is: a full-size, four-wheel-drive pickup truck. For buyers who need the towing and hauling capability of a truck, and who frequently travel long distances, this fuel economy is a genuine advantage, placing it near the top of its class for efficiency.

City and highway performance

The EPA estimates the 2021 GMC Sierra 4WD 3.0L diesel achieves 22 MPG in the city and 26 MPG on the highway. These numbers reflect the characteristics of the engine and the purpose-built nature of this workhorse. The city MPG reflects the weight and inherent inefficiencies of stop-and-go driving in a large vehicle, and the highway MPG demonstrates the engine’s strength and its ability to cruise efficiently once up to speed.

The 10-speed automatic transmission also plays an important role, keeping the engine in its sweet spot for fuel economy at various speeds. Given the Sierra’s size and capability, these numbers are attractive for buyers who want a truck that won’t break the bank at the pump.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2021 GMC Sierra 4WD 3.0L diesel at $2,300. This figure is based on driving 15,000 miles per year and using national average fuel prices. Individual fuel costs will vary depending on driving habits and local fuel prices, of course, but this provides a standardized baseline for comparison. For drivers who rack up even more miles, especially on the highway, the diesel’s efficiency can translate to significant savings compared to a gasoline-powered truck.

Real-world expectations

While EPA estimates provide a useful benchmark, real-world fuel economy can vary. Factors such as driving style, road conditions, payload, and even tire pressure can all affect how many miles you squeeze out of each gallon. Owners who prioritize fuel efficiency and practice smooth acceleration and consistent speeds are more likely to match or even exceed the EPA estimates.

However, those who frequently tow heavy loads or drive aggressively should expect lower numbers. The advantage of the diesel Sierra is that even under load, it tends to maintain relatively respectable fuel economy compared to its gasoline counterparts.

How it compares

The fuel economy of the 2021 GMC Sierra 4WD 3.0L diesel sets it apart from many of its competitors. For example, the Ford F-150 with the 2.7L EcoBoost V6 (4×4), for many years a mileage leader in the segment, achieves around 20 MPG combined. Even the Ram 1500 with its eTorque mild-hybrid system hovers around the same mark, maybe a shade better, depending on engine choice.

Of course, the Sierra’s gasoline V8 options fare worse, typically sitting in the high teens for combined MPG. This difference is significant for buyers who prioritize fuel costs. Someone cross-shopping might also consider the Nissan Titan, but that truck struggles to offer comparable mileage regardless of configuration. The SIERRA MPG across all years demonstrates the consistent advantage this engine offers.

Tips to maximize efficiency

Tire pressure is critical for maximizing fuel economy in any vehicle, but especially in a truck. Regularly check and maintain the recommended tire pressure listed on the doorjamb. Under-inflated tires create more rolling resistance, forcing the engine to work harder and consume more fuel.

Diesel engines tend to reward a steady right foot. Avoid aggressive acceleration and hard braking. Anticipate traffic flow and maintain a consistent speed whenever possible, especially on the highway. This is less stressful in general and greatly improves MPG.

Minimize idling. Diesel engines are more efficient than gasoline engines while idling, but it still burns fuel without covering any distance. If you anticipate being stopped for more than a minute, consider turning off the engine. Modern starters are more than capable of handling frequent starts and stops. Weight is also a major factor in fuel economy. Remove any unnecessary cargo from the bed or cab of the truck. Extra weight forces the engine to work harder, decreasing fuel efficiency.

This is particularly important for buyers who use their trucks for work and accumulate tools in the cab. Avoid using four-wheel drive unless it is truly necessary. Driving in 4WD on dry pavement increases friction and reduces fuel economy. Only engage 4WD when you need the extra traction, such as in snow, mud, or sand.

Remember to periodically check and replace your air filter. A clean air filter ensures that the engine receives an adequate supply of air, which contributes to optimal combustion and fuel efficiency. A clogged air filter restricts airflow, forcing the engine to work harder. You can browse all Gmc fuel economy data.