Should Your GMC Sierra HD Have a Gas-Powered or Diesel 6.6L V8

Many vehicles offer a variety of engine options. One might be larger and more powerful than the other, or nowadays, the more capable choice could be smaller but turbocharged. When considering the heavy-duty GMC trucks at Valley GMC, the decision is between two different internal combustion systems that run on entirely different fuels: gasoline or diesel. Each has its own benefits, so which one is right for you? 

The Sierra HD models come standard with a 6.6-liter V8 gas engine. The engine is straightforward, with no turbochargers, overhead cams, or variable valve timing, but it does feature a modern fuel injection system. It delivers 401 horsepower and 464 lb-ft of torque, with peak torque at 4,000 rpm. This engine is paired with a 10-speed Allison transmission. Since towing is often a primary reason for choosing an HD truck, a Sierra 2500 HD with this engine and a 4×2 drivetrain has a maximum towing capacity of 17,400 pounds for the 2500 and 26,000 pounds for the 3500 models. 

The Duramax turbodiesel is a Sierra HD option, costing just over $10,000 extra. It is also a 6.6-liter V8 and shares the same 10-speed Allison transmission, but that’s where the similarities end. The Duramax is a turbodiesel, and that turbocharger brings in more horsepower than the gas engine, at 470 horsepower. However, the big difference lies in the torque rating, where the Duramax delivers a remarkable 975 lb-ft of peak torque at just 1,600 rpm. Not even the torque-rich Sierra EV has this kind of pull, and it significantly boosts the Sierra HD’s maximum towing capacity, which increases to 22,500 pounds on the 2500 and 36,000 pounds on the 3500 models. If you plan to tow very heavy loads, your choice may already be clear. 

Turbodiesel engines usually have higher fuel mileage than their gas counterparts.  The situation is a bit unclear because HD trucks are not tested for fuel mileage by the EPA, and they don’t provide mpg estimates for heavy-duty trucks. Third-party tests usually show that a diesel achieves around 18 mpg on the highway, compared to 15 mpg for the gas V8, although some have recorded 16 to 17 mpg.  

However, it is notable that diesel engines retain more efficiency when towing heavy loads. So, not only is the Duramax likely to be less stressed when pulling the same weight, but it will probably do so with a lower efficiency penalty. On the other hand, there is a difference in the fuel cost itself. As of this writing, the average price of regular gasoline in Washington is $4.455 per gallon, while the average for diesel is $4.915 per gallon. That is a bump of about 10%, though the difference can be higher in other states.  

The higher fuel costs and the need for diesel exhaust fluid, which costs about $6 per gallon and requires around 2.5 gallons every 300 to 500 miles, combined with an additional $10,000 in the truck’s price and generally higher maintenance expenses, can make owning a diesel engine more costly. However, another factor is that, although diesel engines are more expensive to maintain, they tend to last longer. 

There is no single best choice between diesel and gas engines for an HD truck. A lot depends on how much weight you plan to tow, your expected annual mileage, and how long you want to keep the truck or its engine. That’s why GMC continues to offer both options.  

Consider all these usage factors before choosing the engine for your Sierra HD. Visit Valley GMC, where our sales professionals can give you more details and advice on how you plan to use your HD truck.