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How to Refill Diesel Exhaust Fluid: 4 Easy Tips

Diesel exhaust fluid can usually be found at gas stations that have a diesel pump, like this one.

Using and refilling diesel exhaust fluid (DEF) is increasingly becoming a common aspect of owning a diesel-powered car or truck. This chemical is designed to reduce vehicle emissions by combining with exhaust gases after they have left the engine, which means that, over time, your DEF tank will start to run low. Wondering how to fill your tank, when you need to do so and where you can find the fluid itself? Read on for our DEF tips.

Where Is My DEF Tank Filler?

Most modern diesels position the filler opening for the DEF tank near the diesel fuel tank filler, typically right beside it to make it easy to refill (and to remember to refill). Some older vehicles may locate the DEF filler in the engine bay, the trunk or the passenger compartment itself, which means if you don’t see it when you pop the fuel door, you should consult your manual to find out where you need to look.

Where Can I Buy Diesel Exhaust Fluid?

Diesel exhaust fluid is fairly easy to find at places like your local NAPA Auto Parts store. If you’re on a road trip and find yourself with a warning light telling you your DEF tank is getting low, you can also almost always find DEF at a truck stop or a fuel station that also sells diesel.

Do I Need Any Special Equipment?


Fortunately, the only gear you’ll need to add DEF to your tank is a funnel to help reduce the chances for any potential mess. If you do accidentally spill fluid, you can simply wipe it up with a towel and water. If you happen to find a spill that’s dried into the small white crystals formed by evaporated DEF, this too can be wiped away safely.

How Often Do I Need to Fill My Tank?

There’s no one-size-fits-all answer for how far you can drive before you’ll need to fill your DEF tank. Different engine designs, varying tank sizes and driving habits all determine how long a tank of fluid will last. While your car or truck will alert you when your DEF tank is getting low, consult your owner’s manual or ask your dealer for the average driving window you can expect between fill-ups.

Adding DEF fluid to your diesel-powered rig doesn’t have to be a headache. With these tips in mind, you can find it and fill up in no time.

Check out all the chemical products available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on diesel exhaust fluid, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Flickr.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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