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Does Diesel Exhaust Fluid Go Bad? 5 Common Questions about DEF

Published by JL Mobile Truck & Trailer Repair on 4-17-2024

Does Diesel Exhaust Fluid Go Bad 5 Common Questions About Def

If you drive a diesel-powered vehicle, you may have heard of diesel exhaust fluid, also known as DEF. But what exactly is diesel exhaust fluid and why is it important for your vehicle's operation? In this blog, we will answer some common questions about DEF, including what it is, what it does, what happens if you run out of it, whether it goes bad, and at what temperature it freezes. We will also discuss how DEF diagnostic services provided at a semi-truck repair shop can ensure that your vehicle stays running smoothly.

What is Diesel Exhaust Fluid?

So, let's start with the basics – what is diesel exhaust fluid? DEF is a solution that helps reduce harmful emissions from diesel engines. It is made up of urea and deionized water which is sprayed into the exhaust stream of diesel engines to break down dangerous nitrogen oxide emissions into harmless nitrogen gas and water vapor. This process is called Selective Catalytic Reduction (SCR) and is a mandatory system in all new diesel vehicles to meet emissions standards.

What Does Diesel Exhaust Fluid Do?

So, what does diesel exhaust fluid do? DEF plays a crucial role in reducing harmful emissions from diesel engines. Spraying DEF into the exhaust stream helps convert nitrogen oxide emissions into harmless substances, making diesel engines cleaner and more environmentally friendly. In addition, using DEF can also improve fuel efficiency and engine performance.

What Happens if You Run Out of Diesel Exhaust Fluid?

Now, what happens if you run out of diesel exhaust fluid? Running out of DEF is not only inconvenient, but it can also lead to serious consequences for your vehicle. When the DEF tank runs dry, the vehicle's engine will go into a reduced power mode, limiting its speed and performance. In addition, the vehicle may also display warning lights on the dashboard, indicating that the DEF system needs to be refilled. Therefore, it is crucial to always keep an eye on your DEF levels and refill the tank regularly to avoid any issues.

Does Diesel Exhaust Fluid Go Bad?

Another common question that comes up is, does diesel exhaust fluid go bad? Like any other fluid, DEF has a shelf life and can degrade over time. It is recommended to use DEF within one year of purchase and to store it in a cool, dry place away from direct sunlight. Using expired or contaminated DEF can lead to poor engine performance and increased emissions, so it is important to always use fresh DEF in your vehicle.

At What Temperature Does Diesel Exhaust Fluid Freeze? Can It Freeze While Driving?

Lastly, at what temperature does diesel exhaust fluid freeze? DEF has a freezing point of around 12°F (-11°C), so it is important to take precautions when driving in cold weather. If the DEF solution freezes, it will expand and could potentially damage the DEF tank or lines. To prevent this from happening, it is recommended to use a heater or insulated blanket to keep the DEF tank warm in freezing temperatures.

DEF Diagnostic Services

When it comes to ensuring that your vehicle's DEF system is functioning properly, it is important to have regular maintenance and diagnostic services performed at a semi-truck repair shop. A qualified technician can check the DEF levels, inspect the tank and lines for any leaks or damage, and test the SCR system to ensure it is working correctly. By staying on top of your DEF maintenance, you can keep your diesel vehicle running smoothly and efficiently while also reducing harmful emissions into the environment.


In conclusion, diesel exhaust fluid is an essential component for reducing harmful emissions from diesel engines. By understanding what DEF is, how it works, and how to properly maintain it, you can ensure that your diesel vehicle stays in top condition. If you have any concerns about your DEF system, be sure to visit JL Mobile Truck and Trailer Repair for diagnostic services and repairs. Reach out to us today!

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