What Year Did Duramax Start Using DEF and Why?

Environmental Pollution Agency has made DEF or diesel fluid exhaust compulsory since 2010 in all diesel trucks. Duramax began to use the DEF system in 2011 to till now. Before then, Duramax didn’t use DEF technology in their diesel trucks.

DEF reduces 90% NOx from the exhaust system and increases a diesel truck’s fuel efficiency and horsepower.

What is DEF

Diesel exhaust fluid (DEF) is a mixture of 33% urea and 67% deionized water.

DEF is not a fuel additive. Instead, it’s another type of fuel that reduces 90% of the pollution emitted from the exhaust system of a diesel engine.

DEF is injected into the exhaust system of diesel engine vehicles to turn harmful emissions like NOx gas into Nitrogen and water, which is not harmful to the environment.

This method is known as SCR or Selective Catalytic Reduction.

What Year Did Duramax Start Using DEF?

what year did gm start using def

Environmental Protection Agency, shortly known as EPA. EPA has made it compulsory to use diesel exhaust fluid or DEF in every diesel vehicle since 2010.

All diesel vehicles manufacturer has implemented SCR to meet the standard of EPA after 2010. Duramax started using DEF since 2011 till date.

DEF doesn’t compromise the performance of a diesel vehicle. Rather, it reduces the exhaust system’s carbon dioxide emissions and helps get better fuel mileage and horsepower.

In a word, it enhances the efficiency of a diesel engine to a greater extent but reduces harmful carbon emissions to a greater extent.

How Often do I Need to Add DEF to My Truck

Duramax has 5.3 gallons of DEF tank back of the engine. DEF evaporates after a certain period, but it depends on many factors, including temperature and driving conditions.

If you don’t change, DEF will evaporate, and a low DEF warning will appear on your dashboard. Every container of DEF contains 2.5 gallons of fuel. 2.5 gallons of DEF can last up to 3,000 miles, and 5 gallons will last up to 6,000 miles. You need to buy 2 containers to refill the tank fully.

So, GM advised changing Duramax DEF every 6,000 miles of the drive. Service DEF message will appear, and your truck will go to Limp Mode if you neglect to change DEF.

Why has EPA Made DEF Compulsory?

DEF reduces 90% of the carbon emissions coming out from the exhaust system. So, Environmental Protection Agency has made it compulsory to use the DEF system in every diesel vehicle manufactured after 2010.

DEF can reduce 90% of pollution from a diesel engine. It works like magic. It’s not a fuel additive. DEF is a blue-colored fuel that needs to be filled in another tank to reduce carbon emissions.

Pros and Cons of DEF Truck

Now let’s discuss the pros and cons of DEF and Selective Catalytic Reduction.


  1. Better fuel efficiency.
  2. Reduces 90% NOx emissions.
  3. Increased horsepower.
  4. Produces harmless Nitrogen and water through the exhaust.
  5. Optimized combustion and fewer engine parts wear.
  6. Enhances the longevity of the engine.
  7. Easy to fill the DEF tank.


  1. DEF system of all diesel trucks has manufacturing faults. No truck manufacturer company admits the faults and doesn’t cover DEF under their warranty.
  2. It needs costly maintenance.
  3. Changing DEF fluid in every 6k miles costs around 80 bucks. It’s an extra cost for the truck owners.

Does Temperature Affect DEF?

Yes, temperature fluctuations affect Diesel Exhaust Fluid. The reason is that DEF is composed of 67.5 percent of water and 32.5 percent urea. Therefore, extreme cold or hot temperatures affect the conditions and performance of DEF.

The ideal temperature for DEF is between 12°F and 86°F (-11 and 30°C). If you store DEF at high temperatures like 95°F or more, its shelf life will not be more than 6 months. If you stored DEF at suitable temperature (12-86°F), it can be usable for 1 year or more.

However, DEF shelf life will be 2 years, if the temperature is always lower than 75°F. DEF freezes at 12°F, but modern vehicle comes with advanced Selective Catalytic Reduction (SCR) system that prevents the DEF from freezing.

Can DEF Help to Get Better Fuel Mileage in 6.6 Duramax?

Although Diesel Exhaust Fluid’s (DEF) main function is to reduce emissions, it also helps to improve fuel efficiency. ISO 2241 standard DEF helps the SCR system to perform smoothly and efficiently.

Indirectly it enhances engine performance too. That’s why vehicle fuel mileage increases.

How To Fill DEF Fluid Duramax?

DEF fluid can be added to your vehicle through a filter door. The DEF filter door is located under the hood on the passenger side of vehicles equipped with Duramax engines. It should be a blue cap.

def cap replacement

Follow the steps to fill DEF fluid on Duramax:

  1. Turn off the engine and wait for a few minutes to cool down.
  2. Gather a funnel.
  3. Open the filter door.
  4. There should be a blue cap labeled “DEF.”
  5. Open the cap anti-clockwise.
  6. Now pour the DEF fluid into the container.
  7. You can use a funnel to avoid DEF spills.
  8. Always avoid overfilling.
  9. After filling, tightly screw the blue cap.
  10. Now, start the engine and check the DEF level gauge on the instrument cluster.

Should I Remove My DEF?

No, you should not; your warranty claim will be void if you do so. EPA has made DEF compulsory since 2010 in every diesel truck. Removing DEF means you are breaking the law.

The traffic police will fine you. Most of all, you will be harming the environment by removing the DEF cause it reduces 90% NOx pollution. So, don’t remove the DEF.

DEF has not improved a lot since 2011. It has pros and cons, but overall it’s good to keep the DEF on your truck cause it saves energy and increases your truck’s horsepower and fuel efficiency.

Read More:

Leave a Comment