Everything You Need to Know About DEF

If you drive a diesel car, you may have heard about “DEF fluid.” But what exactly is it, and why should it matter to you?

DEF stands for Diesel Exhaust Fluid, a specialized solution designed to reduce harmful exhaust emissions from diesel engines. It consists of 67.5% deionized water and 32.5% urea, working to convert toxic nitrogen oxides in diesel exhaust into harmless water vapor and nitrogen. This process occurs within a system called Selective Catalytic Reduction (SCR), which has been standard in diesel vehicles manufactured since 2010.

Understanding DEF is essential for diesel vehicle owners. It not only helps maintain your engine’s performance but also reduces your environmental impact and ensures compliance with emissions regulations.

In this blog, we’ll dive deeper into what DEF is and how it works to keep your vehicle running smoothly and responsibly.

What Is Diesel Exhaust Fluid And Why Do You Need It?

DEF, or Diesel Exhaust Fluid, is a colorless, odorless, and non-toxic liquid designed to reduce nitrogen oxide (NOx) emissions in diesel engines. NOx is a harmful pollutant that contributes to smog and respiratory illnesses. DEF works alongside the Selective Catalytic Reduction (SCR) system in diesel engines to convert these toxic emissions into harmless water vapor and nitrogen.

The use of DEF is critical because it helps diesel engines meet stringent emissions regulations imposed by governments worldwide. Without DEF, diesel engines would release significant amounts of harmful emissions, leading to bans in many countries.

Importantly, DEF has no negative impact on your engine. In fact, it enhances both the economic and environmental performance of diesel engines by prioritizing reduced exhaust emissions without compromising functionality.

Also Read: Antifreeze vs. Coolant: What’s the Difference?

How DEF Works in Your Diesel Vehicle

The process of how Diesel Exhaust Fluid (DEF) works is simpler than it might seem. Diesel fuel combustion produces nitrogen oxides (NOx), harmful pollutants that pose risks to both the environment and human health.

DEF is injected into the exhaust stream through the Selective Catalytic Reduction (SCR) system. When exposed to heat, DEF releases ammonia, which reacts chemically with nitrogen oxides in the SCR catalyst. This reaction breaks down the NOx into harmless nitrogen and water vapor. The entire process occurs automatically, ensuring your vehicle’s emissions remain compliant with regulations.

It’s important to note that DEF is never added to diesel fuel. Instead, it’s stored in a separate tank. Running out of DEF won’t damage your engine, but it will activate a reduced power mode until the DEF tank is refilled. This system ensures compliance with emissions standards while maintaining engine performance without added maintenance.

Myths Surrounding DEF

There are several myths about Diesel Exhaust Fluid (DEF) that often confuse diesel vehicle owners.

Myth 1: You Can Substitute Water or Other Materials for DEF.

This is completely false. DEF consists of a precise mixture of urea and deionized water that must meet ISO standards to function properly. Using any substitute will damage your SCR system and void your vehicle warranty.

Myth 2: DEF is Harmful or Hazardous to Handle.

In reality, DEF is biodegradable, non-flammable, and non-toxic. It can be safely handled and stored with standard precautions, making it easy to work with.

Myth 3: DEF Reduces Engine Power.

This is also untrue. DEF interacts only with exhaust gases in the SCR system and does not affect engine performance or speed. To date, no incidents have been reported of DEF impacting engine power.

Understanding these facts will help you avoid costly mistakes and keep your diesel vehicle running smoothly, efficiently, and in compliance with emissions regulations.

How to Know If You're Running Low on DEF

Most modern diesel vehicles are equipped with a sensor to monitor DEF levels and will alert you when it’s time for a refill. You’ll typically see a dashboard light or message notifying you to take action. Ignoring this alert can lead to significant issues.

When the DEF tank gets too low, many vehicles will enter “limp mode,” reducing speed and power until the tank is refilled. In some cases, the engine may not start at all.

Refilling DEF is straightforward. Most gas stations and nearly all truck stops—aside from very basic ones—offer DEF. It’s commonly available in convenient, nozzle-equipped jugs, allowing you to top off your tank easily. Many truck stops also have specialty DEF pumps.

For long-distance travel, it’s a good idea to carry an extra jug of DEF to avoid any disruptions. With proper planning, you can keep your DEF tank topped off and your diesel vehicle running smoothly.

How Often do You Add DEF?

The frequency of refilling Diesel Exhaust Fluid (DEF) depends on your vehicle size and driving habits. On average, DEF consumption is about 2–3% of diesel fuel use.

For heavy-duty trucks, this typically means refilling the DEF tank every 5,000–7,000 miles. For light-duty diesel vehicles, DEF refills are usually needed approximately every 10,000 miles. It’s a good practice to check your DEF levels during routine oil changes or every 2,000 miles, depending on your driving conditions.

Most modern diesel trucks are equipped with a DEF gauge, similar to a fuel gauge, allowing you to monitor your DEF levels. However, vehicles with smaller DEF tanks will require more frequent top-offs.

Keeping your DEF tank full not only ensures your emissions system operates correctly but also prevents frustrating and costly issues, such as engine shutdowns or reduced driveability while on the road.

Will DEF Freeze? How to Handle Frozen DEF

Yes, Diesel Exhaust Fluid (DEF) can freeze at 12°F (-11°C) because it is water-based. However, most diesel vehicles are equipped with DEF tank and line heaters to prevent freezing. Even if DEF does freeze, it will not degrade or lose its effectiveness.

When your vehicle is running, its heaters will warm the DEF, allowing the Selective Catalytic Reduction (SCR) system to function normally.

If you store DEF at home, it’s best to keep it in a garage or another area where temperatures stay above freezing. If DEF does freeze, allow it to thaw naturally—never attempt to speed up the process using hot water or other liquids, as this could damage the SCR system.

Proper storage and understanding how DEF behaves in freezing temperatures can help you avoid winter-related issues and keep your vehicle running smoothly.

Proper Storage Instructions of DEF

Proper storage of Diesel Exhaust Fluid (DEF) is essential to maintain its effectiveness. Always store DEF in its original, sealed container in a dry, cool, and shaded location. Exposure to high temperatures or direct sunlight can cause the urea in DEF to break down, reducing its ability to lower emissions.

When stored correctly, DEF can remain effective for 12 to 24 months. Avoid storing DEF in metal containers, as they can rust and contaminate the fluid. Instead, use clean, uncontaminated plastic containers. Even a tiny amount of dirt or oil can compromise the quality of DEF and damage your vehicle’s Selective Catalytic Reduction (SCR) system.

Always tightly seal the container after each use to prevent contamination. By following these storage guidelines, you can ensure your DEF remains in top condition and continues to support your vehicle’s emissions system effectively.

Run With Senergy for DEF

When you Run With Senergy, you’re not just investing in your vehicle—you’re investing in the future of our planet. The biggest advantage of Diesel Exhaust Fluid (DEF) is its environmental impact. DEF breaks down harmful nitrogen oxides into harmless water vapor and nitrogen, reducing up to 90% of diesel engine exhaust emissions.

This is especially important in cities where diesel exhaust is a major contributor to air pollution and respiratory diseases. With DEF, your diesel vehicle can meet the stringent emission regulations set by governments worldwide, helping reduce the combined impact of transportation on global warming and air pollution.

By choosing DEF, you’re not only staying compliant with emissions laws—you’re also helping create cleaner air for everyone. Plus, the reduction of soot and emissions makes your diesel engine more efficient and longer-lasting, which benefits both the environment and your bottom line.

Run With Senergy and drive cleaner, longer, and more responsibly.

Tagged DEF Fluid, Diesel Exhaust Fluid

PRODUCTS

SERVICES

INDUSTRIES

COMPANY

OUR PARTNERS

LOCATIONS

CUSTOMER PORTAL