Diesel engines are known for their power and efficiency, but they also produce nitrogen oxides (NOx), which are harmful pollutants that are regulated by strict emissions standards.
That’s where Diesel Exhaust Fluid, or DEF, comes in. DEF is a non-toxic solution of urea and water that’s used in Selective Catalytic Reduction (SCR) systems to dramatically reduce NOx emissions.
This article will give you a complete overview of DEF, including how it works, how much you’ll use, and best practices for handling it.
What is Diesel Exhaust Fluid (DEF)?
Diesel Exhaust Fluid, or DEF, is a nontoxic chemical solution made up of 32.5% urea and 67.5% deionized water.
Vehicles with Selective Catalytic Reduction (SCR) systems inject DEF into the exhaust stream. The DEF reacts with nitrogen oxides (NOx) in the exhaust, converting them into harmless nitrogen and water.
To work effectively, DEF must meet quality standards spelled out in ISO 22241.
What affects DEF consumption?
Your DEF consumption rate can vary depending on a few factors:
- Engine size and type. Larger engines need more DEF, and heavy-duty trucks consume more DEF than smaller diesel vehicles.
- Driving conditions and load weight. Stop-and-go driving and frequent acceleration tend to burn through DEF faster than highway driving. Also, the heavier the load you’re hauling, the more DEF you’ll use.
- Driving style. If you tend to drive aggressively, you’ll use more DEF than if you’re driving at a moderate, consistent speed.
Typical DEF Consumption Rates
Generally, you can expect to use about 2 to 3 gallons of diesel exhaust fluid for every 100 gallons of diesel fuel that your vehicle burns. However, this can vary.
For example, a heavy-duty truck might consume as much as 5 gallons of DEF for every 100 gallons of diesel.
To get a more precise estimate for your specific vehicle, check your owner’s manual or consult with a qualified mechanic.
Keeping an eye on your DEF levels
It’s important to keep an eye on your DEF levels. You really don’t want to run out.
Most vehicles that use DEF have a gauge or warning light on the dashboard. Pay attention to it.
If you run out of DEF, your vehicle will likely go into “limp mode,” which means the engine power will be reduced. This is to prevent damage to the system.
How much does DEF cost?
DEF usually costs somewhere between $2.50 and $3.50 per gallon.
Because you have to refill your DEF tank regularly, it’s a good idea to include it in your fuel budget.
There are a few ways to save money on DEF. Buying in bulk is one strategy. Another is using fleet management software to optimize your vehicles’ DEF usage.
Best Practices for Efficient DEF Use
To get the most out of your DEF and ensure your SCR system is running smoothly, follow these guidelines:
Proper Storage
- Store DEF in clean, tightly sealed containers to prevent contamination.
- Keep DEF in a cool, dry area, away from direct sunlight and extreme hot or cold temperatures.
- Be aware that DEF has a shelf life of about 12 months.
SCR System Maintenance
- Regularly inspect the Selective Catalytic Reduction (SCR) system, particularly the DEF injector and catalyst.
- Make sure the system is working as it should to optimize DEF usage and minimize waste.
Using Certified DEF
- Always use DEF that meets ISO 22241 standards.
- Certified DEF ensures you’re using a high-quality product that will perform as expected.
Frequently Asked Questions about Diesel Exhaust Fluid
- What happens if my truck runs out of DEF?
- Your truck might go into limp mode, which reduces engine power and speed.
- Can I mix different brands of DEF?
- Yeah, usually that’s okay, as long as they both meet the ISO 22241 standards.
- How should DEF be stored?
- Keep it in a clean, sealed container, away from direct sunlight and extreme temperatures.
- Does DEF expire?
- It does. DEF usually has a shelf life of about a year.
Frequently Asked Questions
What is a good DEF percentage?
Diesel Exhaust Fluid (DEF) isn’t measured in “percentage” in the way you might be thinking. It’s a chemical solution with a specific concentration. The standard DEF composition is 32.5% urea and 67.5% deionized water. This precise mixture is crucial for the Selective Catalytic Reduction (SCR) system to function correctly. Deviations from this concentration can negatively impact SCR efficiency and potentially damage the system. So, instead of aiming for a “good percentage,” you should always ensure you’re using DEF that meets the ISO 22241 standard, guaranteeing the correct 32.5% urea concentration.
How much DEF to add per gallon?
You don’t “add” DEF to fuel. DEF is stored in a separate tank on your vehicle, never directly mixed with diesel fuel. The SCR system automatically injects DEF into the exhaust stream as needed. The consumption rate of DEF is generally around 2-5% of your diesel fuel consumption. This means for every 100 gallons of diesel you burn, you’ll use approximately 2-5 gallons of DEF. The exact amount varies based on your engine, driving conditions, and the efficiency of your SCR system. Your vehicle’s dashboard will indicate when the DEF tank needs refilling. Always replenish DEF when the warning light appears, ensuring the SCR system operates effectively and avoids potential performance issues or regulatory penalties.
Closing Thoughts
DEF is a critical component for modern diesel vehicles. By reducing harmful NOx emissions, it helps these vehicles meet stringent environmental standards.
To get the most out of DEF, it’s essential to manage it properly. That way, you’ll ensure efficient operation, keep costs down, and avoid potential problems with your vehicle’s emissions system.