Diesel Exhaust Fluid (DEF)

Any conversation about Diesel Exhaust Fluid (DEF) takes us back to 2010, because this was the year when the US Environmental Protection Agency (EPA) created new emission-control standards for medium and heavy-duty vehicles. Manufacturers had to come up with a new vehicular system called SCR (Selective Catalytic Reduction) that reduced oxides of nitrogen (NOx), and used a non-hazardous solution called DEF, which is made up of 32.5% urea and 67.5% de-ionized or distilled water.

DEF is NOT a fuel additive. It never comes in contact with the diesel itself. It is stored in a separate tank with an easily-identifiable blue filler cap, and is sprayed into the exhaust stream of diesel vehicles to break down dangerous NOx emissions into harmless nitrogen and water.

If not managed properly, DEF can become contaminated or degraded and lead to a variety of problems with equipment. Understanding DEF is an integral part of diesel ownership, so we are creating a short FAQ on how to purchase, store and handle this chemical compound in the most efficient manner:

# 1: How Long Can Diesel Exhaust Fluid Be Stored?

The fluid contains no preservatives and therefore cannot be stored for longer than 12 months. This is why small fleets should carefully gauge their Diesel Exhaust Fluid usage. Having DEF in store for more than a year can render it unusable in the future.

# 2: What Is The Best Way To Store DEF?

DEF is corrosive when it comes in contact with aluminum. Store the fluid in ISO-approved containers made from stainless steel, polypropylene or high-density polyethylene. In order to make sure the fluid does not get contaminated, don’t re-use DEF containers. Also, to protect its efficacy, do not pour DEF into some other container.

# 3: What Can Happen If DEF Goes Bad?

Bad DEF can potentially cause damage to components, including engine de-rating or shutdown. The effectiveness of the fluid can be lost, which means you run the risk of going over the legal limits vis-à-vis your NOx emissions. Problems arising from bad DEF can also invalidate any warranty claims relating to your vehicle’s SCR exhaust injection system or catalyst.

# 4: How To Know If Diesel Exhaust Fluid Has Gone Bad?

If the clear liquid seems tinted, cloudy, or has some granularity in it, then the DEF you have in store has gone bad. Dispose of it in an ethical manner.

# 5: How To Buy DEF On The Road?

When on the road, it is often difficult to know if you’re buying DEF that is licensed by API’s Diesel Exhaust Fluid Certification Program. In the absence of brand assurance, look for the expiration date on the container.

# 6: How To Buy DEF For Shop Use?

Always confirm that your DEF supplier is meeting the ISO quality standard and supplying a Certificate of Analysis with every shipment. You can find API-recognized suppliers by clicking HERE.

# 7: Does Freezing Affect DEF?

No. Since it is 2/3 water, it will freeze in colder climates, but that will not affect its performance once it is thawed and made ready for use.

# 8: Does Heat Affect Diesel Exhaust Fluid?

DEF is best stored at a temperature of about 50 degrees Fahrenheit. Direct sunlight harms the fluid, so store it indoors or in cool, shaded areas.

# 9: Does DEF evaporate?

Because of its water content, DEF evaporates if stored at higher temperatures for a prolonged period of time.

# 10: How To Dispense DEF?

Do not use a funnel, pitcher or some other external device to pour Diesel Exhaust Fluid as you will risk contamination. Only pour the fluid directly into the designated DEF tank using the nozzle provided on the storage container.

# 11: Does Handling Diesel Exhaust Fluid Involve Taking Safety Measures?

DEF is a not-toxic, non-flammable fluid. But it’s a chemical compound nonetheless and protecting your eyes and hands is always a good idea. In the event of spillage, DEF is easy to clean up with ordinary detergent and water.

# 12: What is the difference between agricultural urea and the urea used in DEF?

DEF uses automotive-grade urea which is far more pure than fertilizer urea.