What is the gas mileage on a Sierra 2500 6.6 L V8?

The gas mileage for the GMC Sierra 2500HD equipped with the 6.6-liter V8 gasoline engine is typically in the low-teens or high single digits depending on configuration, with most models averaging around 10–12 miles per gallon in combined driving. Exact EPA ratings vary by year, drivetrain, and towing payload.

To understand this question in depth, it helps to recognize that the Sierra 2500HD is a heavy-duty pickup designed for towing and payload, where power and durability often come at the expense of fuel efficiency. The gasoline 6.6L V8 is different from the optional Duramax diesel, and each powertrain has its own mpg profile, especially under load or while towing.

Engine basics

The 6.6-liter V8 gasoline engine in the Sierra 2500HD is a large-displacement powerplant chosen for strong torque and towing capability. It is paired with a heavy-duty automatic transmission and is available with rear- or four-wheel drive. Fuel economy figures reflect the trade-off between power and efficiency, and they are sensitive to payload, towing, terrain, and driving style.

EPA figures and what affects them

What the numbers mean

EPA fuel-economy ratings for the Sierra 2500HD’s gasoline 6.6L V8 vary by model year and configuration. The combined figure is influenced by whether the truck is two-wheel drive (2WD) or four-wheel drive (4WD), as well as axle ratios and whether the vehicle is towing or unladen.

Typical ranges for recent models

In general terms, owners and EPA data for recent model years place the gasoline 6.6L V8 in roughly a 10–12 mpg combined band for 2WD configurations, and slightly lower, around 9–11 mpg combined, for 4WD configurations. Highway fuel economy tends to be higher than city driving, and towing significantly reduces overall mpg compared with unloaded cruising.

Real-world driving and tips

Actual mileage in everyday use can differ from EPA estimates. Factors such as towing weight, payload, terrain, climate, driving habits, and tire choice can push mpg higher or lower. If maximizing efficiency is a priority, consider lightening payload when not towing, maintaining proper tire pressure, using cruise control on highways, and planning routes to minimize stop-and-go driving.

Summary

For the GMC Sierra 2500HD equipped with the 6.6L gasoline V8, expect roughly 10–12 mpg in combined driving under typical non-towing conditions, with 4WD usually on the lower end of that range. When towing or carrying heavy payloads, fuel economy can drop further. Always check the exact EPA ratings for your specific model year, drivetrain, and configuration, and compare them to real-world driving to set expectations accurately. If fuel efficiency is a priority, GM also offers the 6.6L Duramax diesel option, which delivers different mpg characteristics, especially on the highway and under load.

How many miles per gallon does a 6.6 L 8 cylinder get?

A 6.6L V8 gas engine typically gets around 13 to 18 mpg, but this can vary significantly based on factors like driving conditions, towing, and vehicle model. For example, highway driving often yields a better result, around 15-18 mpg or more when not towing, while city driving can drop the average to 13 mpg or lower. 
You can watch this video to see a test of the 6.6L gas engine's highway MPG: 57sGetty's GarageYouTube · Oct 27, 2025
Fuel economy by driving type

• Mixed driving: Around 15-17 mpg. 
• Highway driving: Can be 15-20 mpg or higher, especially with consistent speeds and a 10-speed transmission. 
• 12-13 mpg: City driving: is common, especially with a heavy vehicle.
• Towing: Expect significantly lower mileage, with some drivers reporting 7-13 mpg while towing a trailer. 

Factors that affect MPG

• Towing and load: Hauling heavy loads or towing a trailer will decrease fuel efficiency. 
• Driving habits: Aggressive acceleration and high speeds will lower your mpg. 
• Vehicle specifications: Different truck models, like a 2500HD, will have varying fuel economy figures. 
• Vehicle maintenance: Proper maintenance and tire pressure can help improve mileage. 

This video discusses factors affecting the 6.6L gas engine's MPG: 48sGetty's GarageYouTube · Oct 30, 2025

How many miles per gallon does a Chevy 2500 6.6 get?

A Chevy 2500 with the 6.6L gas engine gets approximately 13 to 16 mpg in mixed driving, but this can vary significantly based on driving conditions and the specific trim level. Some users report lower mileage, especially with heavier loads or after the engine is broken in, while others see slightly better results, especially on the highway.
 
Factors influencing MPG

• Driving conditions: City versus highway driving, speed, and "start and stop" use all affect mileage. 
• Vehicle load: Towing or carrying heavy loads will significantly decrease fuel efficiency. 
• Trim level: Certain trims may have slightly different EPA estimates, though real-world mileage varies. 
• Engine break-in: Early mileage may be lower until the engine is fully broken in. 

Average expected mileage

• Mixed driving: Around 13 to 16 mpg. 
• Highway driving: Closer to 16 to 21 mpg for some trims, but often lower due to the truck's size and weight. 
• Towing: Lower, often in the single digits, depending on the trailer weight and conditions. 

Does the 6.6 gas engine require premium gas?

No, the GM 6.6L gas engine does not require premium fuel; it is designed to run on regular 87 octane gasoline. While a higher octane fuel can be used, the engine's computer will adjust to it without a significant performance boost, and it's unnecessary for the engine's operation.
 

• Regular fuel is sufficient: The GM 6.6L V-8 (L8T) is specifically designed to run on regular gasoline with an octane rating of 87. 
• Premium fuel is not required: You do not need to use premium fuel in this engine, and doing so won't provide a major benefit. It's best to save the extra cost unless the owner's manual specifically states otherwise for a particular model year or configuration. 
• Engine design: The engine's relatively lower compression ratio of 10.8∶110.8 colon 110.8∶1 compared to high-performance engines is why it can handle regular fuel. 
• Check your owner's manual: Although the standard is 87 octane, it's always a good practice to check your specific vehicle's owner's manual to confirm the fuel recommendation. 

What is the life expectancy of a 6.6 L V-8 gas engine?

Overall, the average life expectancy of a 6.6 Duramax engine falls around 200,000 miles or 320,000 km, depending on driving behaviours, usage, and how often the engine is maintained.