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The new reality of handling diesel exhaust fluid

Luke Van Wyk Published on 29 May 2015
DEF container

Over the past few years, refilling with diesel exhaust fluid (DEF) has become a part of regular maintenance on equipment 75 hp and above.

Depending on what machines you run, you may need to refill DEF as frequently as every time you fuel. The challenge is that DEF is different than most fluids we’re used to handling around the farm. Here’s what you need to know.

How DEF came to be

All diesel engines produce the same five emissions: particulate matter (PM), nitrogen oxides (NOx), carbon monoxide, hydrocarbons and heat. Since 1996, when the EPA introduced the Tier Emissions Standards, the focus has been on reducing PM and NOx.

Particulate matter is created when fuel is not completely burned and is composed of small carbon particles and other substances. When nitrogen and oxygen combine at high temperatures they react, and the resulting output is what’s known as nitrogen oxides.

Inside the combustion chamber of a diesel engine, PM and NOx have conflicting chemical factors. When the engine is operating most efficiently for power, minimal PM is produced, but NOx levels are very high.

Diesel engine exhust

When exhaust gas is recirculated back into the intake, NOx production is reduced but higher levels of PM are created. Because of this, no diesel engine can be designed to meet both PM and NOx emission standards without the use of an exhaust treatment system.

Today, all manufacturers of diesel engines larger than 75 hp are using a process called selective catalytic reduction (SCR). SCR injects DEF into the exhaust stream to control and break down the NOx pollutants.

DEF and NOx react and convert to water vapor and nitrogen, which are then released from the equipment’s tailpipe.

The basics of DEF

DEF is 32.5 percent automotive-grade urea and 67.5 percent de-ionized water. It’s a stable, colorless liquid that is non-toxic, non-polluting, non-flammable and non-hazardous.

It is corrosive to most metals and coatings; however, if a small amount is spilled, it can simply be rinsed and wiped up with water.


Temperature affects DEF as it relates to shelf life. Prolonged exposure to direct sunlight and high temperatures will cause DEF to degrade faster. Stored under average temperatures of 50ºF, DEF is good for 36 months.

This reduces to 18 months at 77ºF, 12 months at 86ºF and just six months for DEF consistently exposed to temperatures above 96ºF.

DEF freezes at 12ºF, so follow these guidelines in colder climates:

  • DEF expands by approximately 7 percent when frozen. Prevent fully filled, closed containers and pumping systems from freezing as this can cause damage.

  • Freezing and thawing does not affect the chemical properties of DEF, but be sure the fluid is completely thawed before use.

  • Do not use additives to prevent freezing as this can lead to contamination.


The biggest concern with using DEF in off-road environments is that it is easily contaminated. Direct or airborne contact with as little as one-tenth of a teaspoon of many common elements is enough to bring an entire 5,000-gallon tanker of DEF off-spec according to the ISO 22241 Standard, which outlines the practices for manufacturing and handling the fluid.

Using contaminated DEF can be costly for your operation, both financially and in terms of productivity. Contaminated DEF:

  • Increases DEF consumption in the equipment
  • Loses its effectiveness to remove NOx from engine exhaust
  • Can cause malfunctions with the SCR system
  • Can cause the equipment engine to shut down
  • Can damage equipment
  • Can void a manufacturer’s equipment warranty

Testing for contamination prior to use can prevent downtime and costly repairs. The first indication DEF is off-spec can be judged by the fluid’s appearance. On-spec DEF will be clear with no debris.

Cloudy, discolored fluid or the presence of particles are all indicators the fluid has been contaminated.

You can also purchase handheld testers or refractometers, both of which will confirm a 32.5 percent urea concentration. Finally, and most costly, you can send a sample of the fluid to a certified DEF testing lab for confirmation that it has not been contaminated.

Purchasing DEF

certified label for DEF

DEF is most commonly sold in jugs, 55-gallon drums, 275- or 330-gallon IBC totes and in bulk. Look for the API Certified Diesel Exhaust Fluid logo on product packaging to ensure the fluid was manufactured in accordance with the ISO standard to maintain purity.

DEF is made with a precise ratio of highly pure, automotive-grade urea and de-ionized or distilled water. You should not blend your own DEF using agricultural urea.

Storing and handling DEF

The greatest threat to DEF purity comes from the containers and pumping systems used to store and transport the fluid.

The ISO standard recommends avoiding the following materials:

  • Materials forming compounds as a result of reactions with ammonia, which may negatively interfere with the SCR converter system: carbon steels, zinc-coated carbon steels, mild iron

  • Non-ferrous metals and alloys including copper, copper alloys, zinc, lead

  • Aluminum and aluminum alloys

  • Plastics or metals coated with nickel

Contact with trace elements of any of the following materials will contaminate DEF: copper, zinc, chromium, nickel, iron, aluminum, phosphorous, magnesium, calcium, sodium and potassium.

DEF should be handled in dedicated containers that were manufactured specifically for use with DEF. They should be made with materials approved in the ISO standard and rinsed and sealed accordingly.

Do not reuse or refill open containers and avoid using incorrect dispensing materials such as metal funnels, steel transfer containers, incorrect pumps, seals and fittings.

Ideally, DEF should remain in a closed loop from the supply all the way to machinery in the field. While the standard does allow for open systems, they must be rinsed and flushed between each use.

Since this isn’t practical in off-road environments, closed-loop systems provide the most protection from contamination.

The final step to preventing contamination is to keep the work space clean. Dirt and debris on the equipment and near the fill point can cause contamination.

Purchasing DEF-handling equipment

Here are some things to keep in mind when purchasing DEF-handling equipment:

1. Is the tank and pumping system made in compliance with the ISO 22241 Standard?

2. Is it a closed-loop system?

3. Will the capacity meet my fluid needs?

4. Will a stationary or mobile solution work best for my operation?

5. Do I need a heating solution?

DEF is here

Using DEF in your operation is inevitable. If your equipment doesn’t currently require it, it will in the coming years.

While there has been a fair amount of publicity surrounding the negative aspects of the fluid, there are positives as well. For your operation, SCR technology has led to increased fuel economy.

For all of us, it has drastically reduced emissions that cause pollution.

The reality is: When DEF is handled properly, there is little risk to your operation and machinery. As the old saying goes, “An ounce of prevention is worth a pound of cure.”

Share this article with your team. Proper education will protect your machinery and keep your operation on the move.  FG

Luke Van Wyk
  • Luke Van Wyk

  • General Manager
  • Thunder Creek Equipment
  • Email Luke Van Wyk