Diesel Exhaust Fluid (DEF)

Tips for Avoiding 3 Common Problems with Diesel Exhaust Fluid (DEF)

Every day, the Volvo Construction Equipment technical support team gets calls from customers covering any number of topics. A common engine-related call involves diesel exhaust fluid (DEF). Three issues we see over and over are:

  • Inadvertently putting DEF into the diesel tank
  • DEF contamination
  • Improper handling of DEF

Any one of these is a potentially major issue that can cause significant damage to your equipment. Here’s my advice on how to avoid them.

Don’t confuse fills

Diesel exhaust fluid is an emissions control solution designed to lower the nitrogen oxide emissions in diesel engines. The liquid, which looks like water, is sprayed into the exhaust before it exits the machine.

DEF should never be mixed with diesel fuel, and it has its own filling port. But fuel and DEF tanks are close in proximity on some pieces of construction equipment, so it’s not surprising this mistake occurs. If that happens, and an operator starts a machine with DEF in the fuel lines, it can potentially cause tens of thousands of dollars in damage.

The cap for the DEF tank is blue. If you have machines where the DEF and diesel tanks are near each other, another easy way to tell the difference is the size of the fill holes. Usually, the DEF fill hole is smaller in diameter. If you are ever in doubt if the correct fill hole was used, drain and flush the tank with deionized water or clean DEF fluid.

To avoid running up excessive repair bills, talk to your operators and be sure they know to immediately contact you and your Volvo equipment dealer if they accidentally added DEF to the fuel tank. Your dealer can walk you through the steps to avoid unnecessary damage and the associated costs.

Avoid contamination

DEF is extremely sensitive to contamination — for it to work properly, purity is critical. Contaminants around the fill cap can make their way into DEF and cause damage as well. If the area around the tank and cap isn’t cleaned before the cap is undone and fluid is added, it’s very easy for dirt or dust to fall in and get washed down into the tank. This can cause serious contamination-related issues — and cause unplanned downtime.

The best way to test and monitor the concentration of urea-based DEF is to use a digital refractometer. The ideal concentration is between 32.5 and 37 percent urea. Some signs this ratio may be off and your DEF is contaminated includes an uptick in DEF consumption, the selective catalytic reduction (SCR) system malfunctions or the engine starts shutting down.

These hassles and associated costs can be avoided by simply talking to your operators and maintenance staff to ensure they know how incredibly important it is to clean around the cap before pouring in the fluid. Also make sure they know not to use containers that may have been used for other materials or fluids, even if they’ve been cleaned; DEF should be stored in dedicated containers. DEF is just too sensitive to contamination.

Proper handling

You want to store the DEF out of direct sunlight and in stainless steel or plastic totes as directed by the manufacturer. A cool, dry location indoors is preferred. The DEF will degrade over time but can last up to one year if stored between 12 and 86 degrees Fahrenheit.

DEF will freeze at temperatures below 12 degrees Fahrenheit and could turn slushy, but that does not impact quality or performance. If you are going to keep DEF somewhere cold, you will want an expandable container. DEF expands seven percent once it hits freezing temperature.

To avoid running into storage issues, some operators prefer the 2.5-gallon container over bulk storage to prevent waste and potential contamination.

Other tips

  • Remember to change DEF filters regularly according to service intervals.
  • If the DEF tank is empty, the dashboard indicator light will illuminate and the engine will de-rate after a period of time.

It’s good practice to top off the DEF tank at the end of day. DEF tanks can build condensation, and that water can lead to contamination.

Learn more

We developed this Diesel Exhaust Fluid (DEF) checklist for you and your operators to print out and reference to help avoid these mistakes. Be sure to also follow equipment owners’ manuals and recommendations from your fuel provider.

Article by Rhys Eastham, Director – Uptime & Technical Services


  • Mel

    My DEF doesn’t consume or it stays full even though I drove more than 5,000 miles..the def tank doesn’t consume since I started using an anti gel additives..since December 2018 t haven’t filled up my DEF tank because it stays full..but now, winter is almost over I don’t use diesel additives anymore but instead I use shell diesel oil additives ( to eliminate/ minimize stiction problems).. I keep a close observation about my volvo engine performance,.. or to have a regen warning but it doesn’t show up.. my Volvo engine never slowed down or changed her speed the smoke that go out from exhaust isn’t a black or heavy smoke either.. I called the Volvo remote diagnostic technicians twice and told them about this issue and they told me to observe any red stop sign on the dashboard and they said that as long as the engine is working/running good there’s nothing to worry about… Please give me your opinion with regards to this matter..I’m an owner operator and I don’t want to be ending up in a shop where I will be spending thousand for this problem.
    Thank you.

    April 17, 2019
  • john

    The dash indicator on my 2012 F250 Diesel states that I have 450 miles before my diesel exhaust fluid is empty. Attempt to top off fluid and it overflows as if it is full. What could be the issue?

    June 4, 2019
    • Volvo CE

      Hi John,
      We suggest reaching out to your Ford Dealer to get the best recommendation for this!

      July 2, 2019
  • We are a family run dive centre in Cyprus, we love your content!

    October 3, 2019

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