Things to know about DEF (Diesel Exhaust Fluid) and its Storage

Since the EPA-standardized engines were introduced in 2010, using systems that require fluids to be injected into outgoing exhaust for emission reductions is pretty common. With this in mind, there are some important facts that fleet managers and operators need to know about these fluids, commonly known as diesel exhaust fluids (DEFs). Other common industry names for these fluids include:

  • DEF heavy truck gas tankAUS 32 (Aqueous Urea Solution 32)
  • Catalyst Solution
  • Nitrogen Oxides (NOx) Reduction Agent
  • Urea

All diesel exhaust fluids must conform to the International Standards Organization (ISO) 22241-1. And no acceptable substitute is available. Note: DIN 70070 standard and diesel exhaust fluid specification limits of this standard are identical (ISO) 22241-1.

When a fleet considers purchasing DEF in bulk and storing it, here are a few things to consider:

  • Storage temperature must be in range of 23-77°F (-5-25°C)
  • Has to be in sealed containers to prevent contamination
  • Not stored in direct sunlight

Diesel Exhaust FluidDEF has a minimum expected shelf life of 18 months in these conditions. If DEF is stored at higher temperatures for a prolonged time, shelf life will be decreased by about 6 months for every 9°F (5°C) above the highest storage temperature listed above.

Note that it is not recommended to store DEF in vehicles for over 6 months. If it is necessary to store DEF for a long period of time, perform periodic testing of the DEF to ensure that the concentration does not fall out of specification.

Deisel engine fluidsIt is recommended to use a Diesel Exhaust Fluid Refractometer at the % Urea Concentration: 32.5 ± 1.5%.

Testing should be performed if:

  • The vehicle has been stored for prolonged time
  • You suspect there is an addition of water to the DEF tank

The DEF will freeze around 12°F (-11°C) if the minimum specifications are present.

Also Read:

My DEF Is Frozen! What To Do?

Ultrasound Fluid Testing Helps Detect DEF Quality


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About the Author

Chris Manescu

Chris Manescu joined the Mitchell 1 Commercial Vehicle Group as a Technical Editor in 2010. Chris worked as an ASE certified repair technician for over 20 years after his service in the United States Marine Corps.