How many miles per gallon does a 2003 GMC Sierra 2500 HD engine 6.6 L V8 diesel get?
The 2003 GMC Sierra 2500 HD powered by the 6.6-liter Duramax diesel typically achieves mid-teens to high-teens miles per gallon in mixed driving, with highway fuel economy higher than city driving. Actual mileage varies by drivetrain, payload, and driving conditions.
How the numbers break down by drivetrain
The EPA estimates for the 2003 Sierra 2500 HD with the Duramax LB7 engine show a clear difference between two-wheel drive and four-wheel drive configurations. Here are representative ranges you could expect in typical use:
- 2WD (two-wheel drive) with automatic transmission: City around 14 mpg; highway around 19–20 mpg; combined roughly 16–17 mpg.
- 4x4 (four-wheel drive) with automatic transmission: City around 12–13 mpg; highway around 18–19 mpg; combined roughly 15–16 mpg.
These figures assume standard equipment and tires, with moderate payload. Real-world results can drift up or down based on driving style, load, and maintenance.
Important factors that influence the mileage
Beyond the basic drivetrain, several other variables influence real-world fuel economy for this older heavy-duty diesel pickup:
Key factors
- Payload and towing: Heavier loads increase fuel consumption, especially on hills or when towing.
- Driving conditions and speed: Stop-and-go city driving reduces efficiency; steady highway speeds improve it.
- Tire size and inflation: Larger or underinflated tires raise rolling resistance and hurt mileage.
- Engine and vehicle condition: Air filters, fuel injectors, and exhaust components in good condition help maintain efficiency.
- Maintenance history: Regular oil changes and appropriate lubrication keep the engine operating efficiently.
Owners who keep up with maintenance and drive conservatively at highway speeds typically see mileage closer to the upper end of the ranges above.
Summary
The 2003 GMC Sierra 2500 HD with the 6.6 L Duramax diesel generally delivers about 15–17 mpg combined in typical ownership, with 2WD models leaning toward the higher end and 4x4 models toward the lower end. Highway mileage commonly lands in the 18–20 mpg range, while city use often sits around 12–14 mpg. These figures provide a practical benchmark for fuel costs and planning, though real-world numbers will vary with usage and maintenance.
