Double exhaust from an older car with diesel engine blows out gas with high particulate matter pollution, copy space, selected focus

How to Tell if Your Exhaust Fluid Has Gone Bad

Nearly all diesel-powered vehicles built after 2010 require diesel exhaust fluid (DEF) to reduce harmful NOx emissions. Fortunately, it’s fairly safe and can be stored for a long time. It’s also readily available at a number of diesel exhaust fluid distributors in the event that it goes bad. Here’s how to tell if you need to buy new exhaust fluid.


The easiest way to tell if DEF has gone bad is simple: just look at it! Exhaust fluid is a clear, colorless liquid. If yours appears cloudy or seems to have separated or had any tint, it shouldn’t be used. Be sure to check local regulations to find out how to dispose of it correctly.

Contaminated Liquid

Your diesel exhaust fluid shouldn’t contain any dirt or other particulates. These can damage your SCR (Selective Catalytic Reduction) system and other vehicle components. Once again, it’s usually pretty easy to spot contaminated liquid just by looking at it.

Long Storage

DEF can be stored safely up to a year, so you should have plenty of time to use it up before it goes bad. After this time, however, it may not be as effective, so you’ll want to visit your DEF distributors for new fluid.

Improper Storage

For diesel exhaust fluid to reach its maximum shelf life, it needs to be properly stored. One of the most common mistakes is to store it in areas that get too hot or areas of direct sunlight. Both can be harmful to the fluid. Luckily, it’s pretty impervious to cold. Even if it freezes, it can be used safely after it thaws.

Another important thing to consider when storing your DEF is the container you keep it in. The best way to know it’s properly stored is to keep it in the container it came in. There are very few materials that are approved for DEF storage. Keeping it in the wrong container can cause corrosion, which will then contaminate the fluid.

Why It’s Important

It’s important to learn when to get to your diesel exhaust fluid distributors for new fluid because doing so can have a great effect on how your vehicle operates and how much you have to pay for maintenance and repairs. Old DEF is less effective and you’ll have to pay more as it’s consumed faster by your vehicle. Contaminated fluid may cause malfunctions with your SCR system or damage to your vehicle. Old fluid can even cause your engine to shut down entirely, just as it would if you ran out of DEF altogether.


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