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What Is DEF Fluid? Everything You Need To Know
Diesel exhaust fluid (DEF) ensures that diesel vehicles meet the emissions standards set by the Environmental Protection Agency (EPA).
However, diesel owners may not fully understand the science behind injecting urea into the diesel exhaust stream. This guide explores the role DEF plays in a diesel engine’s emissions system, the problems contaminated DEF can cause, and how to refill and store DEF properly.
What is DEF?
DEF — short for diesel exhaust fluid — is neither a fuel nor a toxic substance. Instead, it’s composed of two components: 32.5% urea and 67.5% deionized water. Maintaining this ratio of urea to deionized water is critical to ensure proper function.
Many diesel owners recognize the popular Peak brand for its Blue DEF product. However, other DEF products are available. Diesel vehicles that require DEF include those that meet emissions standards using a selective catalytic reduction (SCR) system.
How Does DEF Work?
Diesel exhaust fluid (DEF) is one component in a complex system that integrates with the SCR system to lower diesel tailpipe emissions. In addition to the fluid, the DEF system incorporates a DEF tank, heater, pump, lines, and injector nozzle. Each component plays a significant role in the system’s seamless operation.
To understand how the diesel exhaust fluid works, we must first examine the exhaust gases exiting the combustion chamber, which contain nitrogen oxide (NOx). The urea in DEF breaks the chemical bonds between these molecules, separating NOx into nitrogen and oxide to reduce pollution.
In addition, the SCR system measures the appropriate amount of urea to neutralize the NOx in the exhaust gases effectively.
The implications of running out of DEF include more than just emitting more pollution out of the tailpipe. The SCR system will alert the engine control module (ECM) of the lack of DEF, which triggers the ECM to put the diesel engine in limp mode. The ECM will only allow the vehicle to operate normally once the DEF has been topped off.
What Are the Symptoms of Contaminated DEF?
Contaminated DEF can be just as problematic as a lack of DEF, as the two situations result in the same issue: high levels of nitrogen oxide exiting the tailpipe and polluting the air. Thus, it’s important to pay attention to DEF’s condition to ensure it’s functioning properly. A change in color and odor typically indicates the DEF has been contaminated.
Clean DEF can appear clear, slightly yellow, or light blue. Contaminated DEF is cloudy, dark, and has a strong ammonia smell. Performance issues can also indicate the presence of contaminated DEF, including the following:
- Reduced fuel economy
- Excessive DEF consumption
- Elevated emissions output
- Lack of engine power
- Noisy DEF pump or injector(s)
- Check engine light
Dirt, water, metal, and other fluids (like diesel fuel, engine oil, and coolant) can contaminate DEF. Urea also crystallizes once it comes into contact with air, so any leaks in the DEF system can cause the liquid urea to crystallize and harden. These crystals wreak havoc in DEF pumps, lines, and injector nozzles.
In addition, DEF can freeze or gel below 12 degrees Fahrenheit based on the deionized water it contains. DEF systems typically incorporate a heater to prevent this from happening. However, frozen and contaminated DEF have similar effects.
How to Top Off DEF
The rate at which diesels consume DEF is directly related to their fuel consumption. As more fuel is burned, the SCR system requires more DEF.
However, DEF consumption is only roughly 2-3% of fuel consumption, meaning that for every 100 gallons of fuel, diesel requires 2 gallons of DEF. Keep in mind that the DEF tank capacity on half-ton diesel pickups ranges from 2 to 5 gallons, while heavy-duty trucks — like semis — can carry between 10 and 20 gallons of DEF.
Before topping off DEF, check the existing levels so you can adjust your fill amount appropriately.
Several methods exist for checking DEF levels, depending on what provisions the vehicle manufacturer integrated into the system’s design:
- Manually checking the DEF requires locating the dipstick, which is often near the DEF and fuel caps. With your diesel on level ground, remove the dipstick, wipe it clean, and place it back down the fill neck. Slowly remove the dipstick and locate where the fluid sits between the “Full” and “Refill” lines.
- Newer diesels have a dedicated DEF gauge located on one of the main menus in the instrument cluster. This method enables you to easily check DEF levels without leaving the driver’s seat.
- If your diesel isn’t equipped with a dipstick or dedicated electronic DEF gauge, the system may still monitor the DEF levels. Should those levels fall below a specific quantity, the system alerts with a warning light, similar to your check engine light.
Add monitoring your diesel’s DEF levels to your routine maintenance checklist, along with checking other vital fluid levels. When you refill the system, make sure that you use a dedicated funnel or hose to prevent contamination, rendering the DEF unusable.
How To Store DEF Properly
Proper storage of diesel exhaust fluid ensures it will be viable when you are ready to use it. For businesses and diesel owners in Richmond, Virginia, maintaining a clean and properly stored DEF supply is crucial to keeping vehicles compliant and running efficiently. For fleets and diesel operators relying on bulk DEF delivery, proper storage and handling are essential to maintaining performance and compliance. DEF has a shelf life of approximately two years when stored according to the following guidelines:
- Keep DEF in a climate-controlled environment between 12 and 86 degrees Fahrenheit.
- Store DEF in a stainless, rubber, plastic, or titanium container.
- Ensure the DEF containers and storage facility are sealed against moisture.
- DEF containers should also be vented to avoid pressure buildup.
- Place DEF containers in a well-ventilated area away from direct sunlight.
Avoid funnels when transferring DEF between containers. Instead, use a dedicated hose or system to protect against contamination. Should DEF become contaminated, dispose of it properly according to local hazardous waste disposal guidelines.
Source Top-Shelf DEF from Cadence for Your Diesel
Cadence offers the broadest range of diesel exhaust fluid products nationwide. Partner with us to experience the unmatched quality and service that comes from delivering value at every turn.
Call us at 336-629-2061 to discuss obtaining a high-quality DEF supply through Cadence’s partnerships with esteemed manufacturers.
Sources:
Facts About… - Selective Catalytic Reduction (SCR) | Maryland Department of the Environment
Diesel Exhaust Fluid (DEF) | API