​​What is DEF​? Why is it Important for Your Diesel-Powered Vehicle?

We all love the sound of diesel engines. However, many of us could do without the “smoke” that comes out of its exhaust. 

In modern diesel-powered vehicles, an emissions mandate now requires the tailpipe to be cleaner. That is why you are seeing a lot of pumps at the gas station and containers carrying DEF, or Diesel Exhaust Fluid.  

What exactly is DEF? According to the Diesel Power Products website, it is “a fluid that gets injected into the exhaust system of your truck to help reduce pollution.” It is composed of 67% deionized water, with the remaining 33% derived from a source called urea. “Urea is a natural byproduct of the metabolic process that takes place within a cell, and it’s abundantly found in nature.” 

DEF does work to keep the exhaust clean. But how? 

Diesel Power Products explains that “when diesel fuel is burned inside your engine, it creates heat and horsepower. The horsepower is used to move the vehicle along, and the heat is dealt with through the radiator, but there are also several other unwanted byproducts that are a result of the combustion process. Because diesel fuel is a hydrocarbon, when it’s burned, there are two major pollutants that come out of the tailpipe of the truck, which are nitrogen oxides (NOx) and particulate matter (PM), which is basically soot or black smoke.”

In 2008, vehicles with diesel-fueled engines were fitted with a diesel particulate filter, which traps soot from escaping the tailpipe. Two years later, Selective Catalyst Reduction was added to the exhaust mix. That is where the DEF goes after it is filled into its own tank. 

A DEF tank holds five gallons. From there, it goes through a system with a pump and lines, eventually feeding the exhaust system. With a command from the engine control module, an injector nozzle sprays the exact amount of DEF needed into the exhaust system. If you’re worried about it freezing up in the winter, the tank and DEF system are heated.  

Of course, you need to ensure that you have enough DEF to keep your diesel-fueled vehicle’s exhaust clean. How long should you have DEF in its tank? And when do you refill it? 

It has been said that the consumption of DEF is almost equal to the actual fuel mileage. However, the DEF tank only holds five gallons. Luckily, modern pickup trucks have readouts that indicate the amount of DEF in the tank and the distance until the next refill is needed. Since there is not a gauge that is immediately available to read, you would have to go into the instrument cluster menus to get that readout. Some vehicles have a message that will pop up telling you when you should fill the DEF tank, along with its remaining range before it empties.  

DEF is available in containers that you can buy from auto parts stores or truck equipment dealers. These containers should be stored in a clean, climate-controlled area. Preferably between 23-86 degrees Fahrenheit. There are also DEF pumps available at select truck stops that you pull up and fill ‘er up.  

What if something goes wrong with your DEF system or any exhaust system components on your diesel vehicle? That is where Alderman Automotive’s Service Department comes in. We can help you by performing the necessary repairs to prevent your diesel-engined vehicle from emitting any black smoke from the tailpipe. If that happens, set up an appointment with us and we’ll get you back on the road cleaner than ever.