12 Tips on How to Get Better Fuel Mileage in a 6.6 Duramax

Fuel mileage is always a great concern for many owners. Especially when it comes to a heavy-duty vehicle, fuel mileage like Duramax 6.6L engine owners always want to know how to get better fuel mileage in a 6.6 Duramax engine.

If you are one of them, congratulations! You are in the right place. In this article, I have discussed the 12 different methods that improve your Duramax 6.6-liter engine’s fuel mileage.

What is the Fuel Mileage for a 6.6 Duramax Diesel?

Duramax 6.6 engine is used in various GM trucks, including Chevrolet Silverado, GMC Sierra, GMC Savana, and Chevrolet Express. They are different models of GM trucks, so they have different mileage.

On average, the fuel mileage of Duramax 6.6 Diesel is 22 MPG on the highway and 18 MPG in the city.

How to Calculate Gas Mileage

A vehicle’s gas mileage depends on several factors. Therefore, before attempting to enhance your vehicle’s mpg, it is necessary to determine the current mpg.

So, let’s find it:

  • Completely fill up the vehicle’s tank.
  • Reset the vehicle’s trip odometer.
  • Use at least half of a gas tank while driving.
  • Now, refill vehicle’s tank to the fullest capacity.
  • Note the amount of gas required for refilling.
  • Now determine the distance you have traveled by using the start and current odometer.

Follow the equation to find out, Gas Mileage = Total Distance ÷ Amount of Gas Required. For example, if you traveled 120 miles and it required 8 gallons to refill, then the vehicle gets 15 mpg.

How to Get Better Fuel Mileage in a 6.6 Duramax

The mileage of the Duramax engine varies from model to model. The average mileage of a 6.6 Duramax is 22 mpg on the highways and 18 mpg in cities. If your mileage is below this range, here are 12 tips to get better fuel mileage in your Duramax.

1. Tire Pressure

You should know that tire pressure is an important factor in fuel mileage. According to the U.S. Department of Energy data, fuel mileage decreases by 0.4% for every 01 psi drop in tire pressure.

In this sense, Duramax trucks’ tire pressure decreases by 40% from the recommended level, increasing fuel consumption by around 8%. GM-recommended tire pressure is 30 psi for the front and 35 psi for the rear tires.

But as a mechanic, I recommend keeping all tires at the same pressure for good fuel mileage. Even keeping 3-5 psi higher than the guideline is better.

This is because the tire pressure naturally drops 1-2 psi per month, and 1-2 psi drops for every 10-degree temperature drop in cold weather. So, keep all your tire pressure at 35psi for better fuel mileage in your 6.6 Duramax.

2. Drive in Economic/2WD Mode

6.6 Duramax is equipped with 2WD and 4WD options. The 4-wheel option is used for off-road driving as it improves driving performance in certain conditions.

If you are stuck in mud or a hill, use 4WD mode to get out of the uncomfortable situation. But 4-wheel consumed extra fuel as it needs more power. In normal conditions, always drive in 2WD or economic mode. It will increase your vehicle’s fuel mileage.

Because in 4WD mode, some components like the front driveshaft, front side-shafts, front axle, front wheels, transfer case, etc, are actively working and cause extra fuel consumption.

3. Use Premium Grade Diesel

A premium #1-grade diesel provides better fuel mileage and power than regular #2 diesel. It works as an engine cleaner and helps the engine to run more proficiently.

According to some tests, a premium-grade diesel increases an engine’s power by about 4.5 percent and fuel economy by 5 percent compared to regular diesel. At present, Premium-grade diesel is available all over America.

A premium diesel will provide you 5 benefits, including-

  1. Quicker start-ups
  2. Keep your engine clean
  3. Reduce friction
  4. Keep unwanted moisture out
  5. Prevent deposits

So, use grade #1 premium diesel in your Duramax for extra fuel mileage and engine efficiency.

4. Change Engine Oil In Every 6000 Miles

Always use synthetic oil for your engine. For synthetic engine oil in Duramax, it is recommended to change it every 6000 miles.

Synthetic engine oil will provide 07 benefits.

  1. Keep the engine clean
  2. Form a seal
  3. Prevent corrosion
  4. Keep engine parts excellent
  5. Dampen shock
  6. Transfer energy
  7. Reduce wear and minimize friction between most of the engine parts

But if you use conventional or semi-synthetic engine oil, you must change the engine oil every 4000 miles.

5. Change Air Filter In Every 15,000 Miles

For the combustion process, an engine needs oxygen. The air filter provides fresh air to the engine by preventing particles, dust, debris, and insects. An air filter determines the proper mixture of air and fuel for better engine performance.

After reaching around 15,000 miles, the air filter fills with dust and filth, and its performance reduces to a great extent. So, it is important to change the air filter of your Duramax every 15,000 miles.

There are 6 benefits of changing the air filter in your Duramax 6.6.

  1. For better engine performance
  2. For better fuel economy
  3. It will prevent black smoke
  4. Improve the internal air quality
  5. Make your HVAC system last longer
  6. Reduced repair cost.

6. Add DEF Fluid Before it Becomes Less than 5%

A DEF is a solution of 32.8 percent of urea and 67.2 percent deionized water. Diesel exhaust fluid (DEF) reduces around 90 percent of the pollution emitted from engine exhaust systems and increases the fuel mileage of an engine.

Your vehicle will go to Limp Mode if the DEF fluid is less than 5%. So, add DEF fluid before it become less than 5%.

DEF provides you with the following 06 benefits.

  1. Increase fuel mileage
  2. Reduced maintenance
  3. Optimized combustion
  4. Safer emission
  5. Fewer regenerations
  6. Better reliability

7. Change the Glow Plug Every 100000 Miles

Unlike petrol engines, there is no spark plug in Duramax 6.6 diesel engine. Instead of spark plugs, Duramax 6.6 diesel use compression ignition and glow plugs.

Glow plugs of diesel engines heat the air in the combustion chamber for the engines faster start in cold weather. If the glow plugs fail, occasionally, the engine will fail to start in cold weather.

Fresh Glow plugs increase engine performance and fuel economy overall, while bad glow plugs reduce engine performance and fuel mileage. A glow plug fails because of wear and tear in the air.

It is recommended to change the glow plug set every 100,000 miles. Changing the whole set is recommended because changing 2-3 faulty glow plugs doesn’t get many benefits, and soon problems appear in others.

There are 08 glow plugs in Duramax. Changing the whole set is beneficial and not very costly. It just costs you around 250$ to 300$.

8. Change All Brake Pads Every 30,000 Miles

Brake pads should be replaced every 30,000 miles for better performance and fuel efficiency. If you found the following 06 symptoms, you should replace the brake pads immediately-

6 symptoms of brake pad failure.

  1. Squealing or squeaking noise
  2. Grinding sound
  3. Vibration when braking
  4. The brake pad indicator light pops up
  5. Spongy brake
  6. Longer brake distance.

Change the brake pads immediately if you notice any symptoms. If there is any problem with one of the front or rear brake pads, replace both brake pads, either front or rear. This will save you from the hassle of frequent brake pad maintenance.

9. Don’t Neglect Warning Signs

A warning sign gives a message about specific problems. Red and Orange are two types of dashboard warning signs (Green is a safe sign). The Red warning light generally indicates serious issues. Different types of warning lights appear on a vehicle’s dashboard.

Among them, 05 signs indicate serious problems which should not be avoided.

  1. Check the engine warning sign
  2. Oil pressure warning sign
  3. Tire pressure warning sign
  4. Electrical system fault warning sign
  5. Coolant temperature warning light

A vehicle engine is a complex machine, and each engine part is related to others. If one problem is ignored, it will lead to another problem. Don’t expect good fuel mileage with a red or orange warning sign.

So, don’t ignore warning signs and take the necessary steps as soon as possible to enjoy a good fuel mileage.

10. Don’t Idle Unnecessarily

Unnecessarily idling consumes fuel and decreases fuel economy, creates pollution, and costs you money. Because of idling, your truck loses around a half gallon of fuel every hour. So, switch off your engine if you stop anywhere for more than 5 minutes.

11. Lower Air Conditioner Use

To get better fuel mileage, stop using air conditioners unnecessarily. An air conditioner overpressure the engine and decreases the engine’s overall performance and fuel economy.

Research says AC consumes 15% to 20% extra fuel. So, in normal conditions, turn off the AC to enjoy good fuel mileage in your Duramax.

12. Go to Your Dealer and Do a Basic Check Up in Every 15,000 Miles

A driver should usually complete a routine truck check at the beginning of the work day.

Generally, truck companies divide their truck’s service schedule into 03 categories, basic, thorough, and complete service.

  • Basic checking/service every 15,000 miles
  • Thorough service every 30,000 miles and
  • Full service every 12 months or once per year.

05 different services are included in the basic check-

  1. Checking engine oil and filters;
  2. Engine other fluid levels;
  3. Checking tire pressure;
  4. Inspect your brakes;
  5. Verify the electrical system;
  6. Inspect your gearbox and clutch.

Regular maintenance keeps your vehicle updated and provides better fuel economy.


How do I get the best mpg on my Duramax?

Smart driving habits and strategic modifications can increase your Duramax’s mpg. For the latest Duramax engines, the following modifications and maintenance are recommended:

  • Do not use AC, when not needed.
  • Install a bed cover.
  • Tune the engine.
  • Install a new fuel filter.
  • Air intake upgrades.
  • Tailgate removing.

Does a turbo increase MPG?

Turbo does not directly connect with MPG. Turbo is able to increase horsepower and possibly increase highway mpg, without increasing engine size.

But they consume more fuel when require high accelerations. That’s why a few additional criteria and your driving style will mainly influence your vehicle mpg.

Does removing muffler increase mpg?

Removing muffler doesn’t impact on the MPG. But there is a high chance of decreasing fuel economy, if you remove the muffler. You should consult with a nearby professional mechanic before doing so.

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