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Educate Yourself | Everything You Need To Know About Diesel Exhaust Fluid or DEF


Educate Yourself | Everything You Need To Know About Diesel Exhaust Fluid or DEF

With an increasing number of Tier 4 Final engines in use, diesel exhaust fluid (DEF) has joined the ranks of must-have maintenance products. New heavy construction equipment and trucks use DEF in their selective catalytic reduction (SCR) systems. Industry experts predict that by 2025, demand for DEF will have tripled, reaching 1.8 billion gallons. No doubt some of that demand will come from your dealership and your customers.

With that in mind, this is a good time to take a closer look at diesel exhaust fluid.

What is it?

diesel-exhaust-fluid-DEFSelective catalytic reduction is a technology that was developed in response to dramatically tightened federal emissions regulations for heavy-duty diesel engines. Although diesel fuel is now formulated to burn cleaner, an SCR system treats the engine exhaust as an additional final step. The system sprays a controlled amount of DEF into the exhaust, where it reacts with nitrous oxide (NOx). The result is nitrogen and water, both of which are harmlessly released into the atmosphere.

DEF purity is critical

DEF is 32.5% automotive grade urea and 67.5% water. It’s a clear, non-toxic liquid. However it can corrode some metals, including, zinc, nickel, iron, steel, copper, magnesium and aluminum. DEF can easily become contaminated by chemical impurities. Therefore, improper storage or handling of DEF can harm your Tier 4 engine.

ISO standard 22241 states that a 5,000 gallon tank of DEF can go off-spec with the addition of just 1/10 of a teaspoon of any of these elements:

  • Educate-Yourself-Everything-You-Need-To-Know-About-Diesel-Exhaust-Fluid-or-DEF-2Aluminum
  • Calcium
  • Chromium
  • Copper
  • Iron
  • Magnesium
  • Nickel
  • Phosphorous
  • Potassium
  • Sodium
  • Zinc

Tap water can also cause problems if it gets into your DEF supply. In turn, contaminated DEF can create problems from rendering your SCR system ineffective to engine de-rating and shutdown. Resulting damage won’t be covered by your warranty if the manufacturer can trace the problem back to your use of contaminated diesel exhaust fluid.

Clearly, the best option is to protect your engine by protecting your DEF.

Extending DEF life

Diesel exhaust fluid will degrade over time if it is exposed to high temperatures or direct sunlight. Ideal storage temperature is around 50o F, in which case the product should last about 36 months. But life expectancy plummets under consistently higher temperatures:

  • 18 months at 77o F
  • 12 months at 86o F
  • 6 months at 96o F

MHC_CTL_6-22-11_photo_C232_snowWhat about winter? The freezing temperature of DEF is 12o F. Freezing won’t hurt it, but it could harm your storage container or pumping system. That’s because, like water, DEF expands when it freezes – about 7%. So a full container or pumping system could burst. You can prevent this by protecting storage and pumping systems from freezing. You can add heating elements to mobile pumping systems. You can also choose a 2-in-1 system that draws unused DEF back into the container after pumping.

Never use DEF until it is completely thawed. And never use additives to keep it from freezing.

Buying and storing DEF

You can purchase DEF is very small to very large quantities, depending on your needs:

  • Jugs
  • 55-gallon drums
  • 275- or 330-gallon intermediate bulk container totes
  • Bulk supplies

Before you purchase, always check the label to be sure it meets ISO standard 22241. Never mix your own DEF.

Use only storage containers specifically constructed to hold DEF. The materials should meet ISO standards, and the container should be sterilized and sealed. Never use a container that previously held some other product.

You can use open systems, but due to the possibility of contamination, most manufacturers recommend using closed systems. (Open systems also have to be re-sterilized between each use. This takes up time and isn’t necessarily possible at worksites.) Open and closed systems can be used in conjunction with a 50-gallon tote, or you can purchase an ISO-compliant DEF trailer for transport. Some other types of fuel or service trailers can also accommodate DEF systems.

Properly storing and handling diesel exhaust fluid will help keep your Tier 4 construction equipment and trucks running smoothly and productively.


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