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Before we start, here’s a quick review of Deisel Exhaust Fluid. DEF is designed to treat exhaust coming through the exhaust chamber to meet emissions that were implemented in 2010. Basically, the government issued mandates for lower emissions from diesel engines. DEF uses a mixture of Urea (32.5%) and water (67.5%) sprayed on the exhaust fumes which reduces the NOx to nitrogen and water in order to meet the recommended levels. Since my last article on DEF for Coach-Net was published we have been getting numerous questions regarding DEF and its shelf life, how we know if it’s contaminated, and how to get rid of it.

Is There A Shelf Life For DEF?

I talked with a representative from Blue Sky that stated their DEF has a general one-year shelf life. They went on to state that the Urea will degrade if exposed to direct sunlight or stored in temperatures above 90 degrees. The actual amount of degradation can not be determined unless you purchase a DEF tester.

The representative went on to clarify that if the DEF is stored between temperatures of 10 degrees to 90 degrees it has a one-year shelf life BUT if it is kept out of sunlight and under 75 degrees, it can be used for up to two years, however, it’s best not to use it if it’s over 3 years old.

I have run a company for the past 10 years that had 3 diesel trucks pulling trailers that put over 100,000 miles on each vehicle every year, therefore we have had lots of experience and education regarding DEF. In face, we received a service notice from Ford Motor Company on DEF Shelf Life vs Temperature which listed the following:

Constant Ambient Storage Temperature / Shelf Life In Months

  • ≤ 50 °F degrees – 36 months
  • < 77 °F degrees – 18 months
  • ≤ 86 °F degrees – 12 months
  • ≤ 95 °F degrees – 6 months
  • < 104 °F degrees – 2 months

Interpreting DEF Codes

How do you know when your DEF was produced in order to determine its shelf life? Off-the-shelf products such as the 2.5-gallon versions have a code on the box that includes a date stamp. However, these codes can be difficult to decipher.

I talked with Peak Technical Product Support and he said there are many different codes used on their product due to the bottling and packaging at different plants all over the country. He dissected this one for me as follows:

23/169 /CP7/ 00591/ 0125

  • 23 is a year minus 1 year=2022
  • 169 is how many days are left in the year 2022=July 15, 2022
  • Cp7 is the bottling plant
  • 00591 is tank number
  • 0125 is the batch number

He also stated that they have a two-year shelf life recommendation however it was best to purchase a digital refractometer to be sure what you are putting in your tank has not expired. If you have any doubts as to the date code recommend, call their tech support number and a technician will help dissect the code for you. He also stated that both Walmart and Home Depot are the largest distributors and would have the newest product.

DEF Life At The Pump

Ok, but what about the DEF that is pumped at a larger fueling station from an underground tank and does not have anything printed? The easiest way to tell if the DEF has expired or been contaminated is by looking at it. When DEF is in good shape, it should look clear and free of any contaminants or discoloration. If it is cloudy, discolored, or difficult to see through, it is likely expired.

I spoke with a technician at Cummins and they stated that The NOx sensors monitor the DEF quality and will provide an indication when DEF is not in compliance which is the check engine light.

So what happens if you do have a full tank of DEF and the dreaded “Check Engine” light shows? There are service centers that will drain the tank for you however it can be expensive. Alternatively, you can do it yourself with a mechanical pump or even a hand pump depending on how much you have in the tank. If you have a truck the DEF tank will only be about 3-4 gallons which can be pumped out with a hand pump and put in an empty DEF container or gallon jugs.

According to Daimler Worldwide and specifically the Freightliner Custom Chassis Corporation (FCCC):

DEF life will vary based on temp and direct sunlight, so having the tank in a compartment like it is on RVs is much better than on a vehicle where the tank is exposed to direct sunlight. FCCC has not seen a large number of people having an issue with DEF quality, but I would recommend always leaving some room in the tank so that if you do get an indicator you can still put some fresh DEF in the tank and help revive the DEF quality. In some cases service centers have had to force air into the tank with a hose and then have a second hose to allow it to drain, but that’s certainly not the norm.

What Do You Do If You Have Expired DEF In Your Tank?

So if the shelf life is one year, what should we do about units that have DEF sitting in the tank for longer than that? I’ve talked with several owners who stored their rig during the pandemic and their DEF could be 2-3 years old! As FCCC indicated, try to leave the tank less than ½ full as you can strengthen or rejuvenate degraded DEF with the addition of new DEF!

Being from the Midwest, I contacted the local farm equipment dealer as well as PetroBlend, one of the largest distributors of DEF in the agricultural industry. They stated the very same thing that proper DEF management is the key, as sometimes combines will not go through their 30-gallon tank for a couple of years.

Where Can You Properly Dispose Of Bad DEF?

The internet is flooded with DEF information with some stating it is the same chemical composition as fertilizer so you can dump it just about anywhere. While DEF is non toxic, it should be disposed of in an environmentally friendly way. Do not pour bad DEF down the drain or dump it on the side of the road. It’s recommended to contact your local environmental waste disposal company for a nearby disposal site. I also called the local landfill as they have a hazardous materials division and they will take it at no cost as it is considered residential and falls under fertilizer or engine fluids. Anything over 10 gallons is considered commercial and assessed per gallon.


About the author: Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles authored an RV handbook reference guide, and logged over 100,000 miles on the road in an RV.

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