Everything You Need To Know About Diesel Exhaust Fluid Caps

October 25, 2018
min read

Diesel exhaust fluid caps allow you to refill the engine’s DEF, also known as emission fluids. While it may sound like one of those joke or mythical items, like blinker fluid that have confused many over the years, it is a necessary and real product that manufacturers have created. They now use SCR (selective catalytic reduction) to help reduce nitrous oxide emissions. In past years, EGR was used to help reduce the NOx emissions, but EGR can affect the combustion and may create a lower fuel efficiency. SCR can help you use less fuel and helps the vehicle run smoother.  

More About SCR And DEF

The selective catalytic reduction system uses a spray version of DEF, which is a mixture of urea and de-ionized water, into your catalytic converter. It then reacts with the nitrous oxide and turns it into a harmless nitrogen/water mixture. DEF is sprayed at approximately two or three percent of your fuel usage rate and is stored in a tank that must be refilled every three months or so. Most people tend to refill their DEF when they change their oil.
To refill the diesel exhaust fluid, you’ll have to twist off the cap, which is usually found next to the fuel filler cap behind the fuel door. Sometimes, DEF caps are placed under the hood of the truck or in the trunk. Sometimes, they can be locked to prevent tampering and theft.

When To Replace The Cap And How?

Diesel exhaust fluid caps helps to keep fluid inside your tank, but can also keep debris and dirt out. Over time, it may develop a slight leak or crack, allowing some dirt to get inside. Likewise, it can cause the liquid to evaporate at a faster rate, causing it to need to be refilled more frequently.
Over time, the dirt that got into the DEF will settle into the catalytic converter, which makes it less efficient. It can also lead to you failing your emissions test. Likewise, DEF may not be toxic, but can still corrode metals, so if you notice leaks, you should have them checked out and fixed as soon as possible.
Likewise, you can replace your DEF cap yourself. All you have to do is find a suitable replacement cap, remove the old one, remove the strap holding it in place, then put on the new one, strap it on, and twist it shut.


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