November 14, 2016

Defining DEF

Of the many acronyms associated with emissions technology, DEF is one you definitely need to know. Below you will find some useful DEF information, including where you can buy it, and how to properly handle and store the fluid.

What is DEF?

DEF, or diesel exhaust fluid, is used in a selective catalytic reduction (SCR) system to remove nitrogen oxides (NOx) from engine exhaust. The main components of the SCR system include the SCR catalyst, the DEF injector, the DEF tank, and the DEF supply module and filter (see image below). DEF is injected into the exhaust stream prior to the SCR catalyst. NOx in the exhaust stream is then converted into harmless nitrogen and water through a chemical reaction.

DEF is 32.5 percent DEF-grade urea and 67.5 percent demineralized water. This ratio provides the lowest possible freeze point.

DEF is also:

  • Colorless
  • Nonflammable
  • Nontoxic
  • Slightly corrosive
  • 9.1 lb./gal.

Many names and terms are used for DEF:

  • Urea
  • Aqueous urea solution – AUS32®*
  • AdBlue®**
  • NOx reduction agent – ARLA 32TM
  • Diesel exhaust fluid

Where do I purchase DEF?

Similar to oils, coolants, lubricants and transmission fluids you currently use, DEF is available in a variety of containers sizes. John Deere dealers selling Final Tier 4 equipment carry DEF and will assist you to find the appropriate amount for your machine.

The best way to ensure you are getting high-quality DEF for your engine or equipment is to purchase DEF through your John Deere dealer. When you buy DEF from John Deere, you can be confident you are getting a high-quality product that will provide maximum performance while protecting your engine investment. Other DEF brands may be used only if they meet one or more of the following certifications:

How often will users need to fill tanks with DEF?

DEF consumption is primarily based on engine loads and engine speed. Typically, the DEF tank should be checked and filled as part of your normal service checks. The DEF filling port is identified by a blue-colored cap embossed with the DEF symbol.

IMPORTANT: Never put DEF in a diesel fuel tank.

How should DEF be stored?

DEF should be stored in sealed containers to avoid contamination and evaporation. Only use containers made of DEF-compatible stainless steel, high-density polyethylene or polypropylene, as DEF can be corrosive to certain materials such as steel, iron, zinc, nickel, copper, aluminum, and magnesium. DEF contamination, even with trace amounts of metals, can damage the catalyst in the SCR system.

What happens when DEF freezes?

DEF begins to freeze at 12° F (-11° C), but even if it freezes solid, it can be used when thawed.

DEF expands approximately 7 percent by volume when frozen. Allow room for expansion in storage containers and make sure residual DEF is removed from pumps, nozzles, and hoses. Do not use antifreeze fluid products to winterize pumps, nozzles, and hoses as the residual antifreeze fluid can damage the SCR system.

On the engine or equipment, the DEF tank itself is equipped with a heating element that utilizes engine coolant to thaw DEF in temperatures below 12° F (-11° C). The engine can be operated immediately and throughout the DEF tank thawing process.

Do not add any chemicals or additives to DEF in an effort to prevent freezing. Adding chemicals can damage the aftertreatment system.

*AUS32 is a registered trademark of GBZI LTD.
**AdBlue is a registered trademark of VDA, the German Association of the Automotive Industry.