You may have heard someone joke about filling up your blinker fluid in a car. Blinker fluid of course doesn’t exist, and while diesel exhaust fluid may sound like a joke, its not. If you’re looking into purchasing a diesel truck, you might see the need for using a specific fluid and wonder, “What is DEF fluid?” You’ve never had to put this kind of fluid into your gas vehicle before. This is one of the bigger differences between a gas and diesel engine truck, and understanding why it’s important to owning a diesel engine truck. Let’s dive in to what is diesel exhaust fluid.
What Is Diesel Exhaust Fluid?
Diesel Exhaust Fluid (DEF) is used in diesel engines. In 2008, the Environmental Protection Agency (EPA) issued a mandate requiring the use of diesel particulate filters on all on-road diesel engines.
In chemical terms, it’s a mixture of 67.5% deionized water and 32.5% urea. When the urea is heated, it turns to ammonia. It’s a colorless odorless fluid that usually comes in a blue jug and is called ad blue in Europe. While it generally is non-toxic it can crystalize and make a mess if spilled.
DEF is a mixture sprayed into the exhaust system of diesel trucks. If may seem weird but yes the fluid is pumped into the exhaust just before the catalytic converter to facilitate a reaction that breaks down the generated nitrogen oxides (NOx) into harmless nitrogen and water molecules. Manufacturers use DEF to abide by the EPA’s guidelines.
What Is the Difference Between a Gas Engine and a Diesel Engine?
Diesel and Gas engines in vehicles are more similar than they are different. They are both four-stroke internal combustion engines that use liquid fuel and share most of the same basic operating principles however there are a few major differences.
Gas and diesel engines both convert fuel into rotational motion via internal combustion pistons. Because diesel fuel is thicker and has more energy density than gasoline, diesel engines operate with about 20% more thermal efficiency than gas engines. This increase translates to more power and torque per fuel used.
A spark controls the gas engine, which ignites the fuel and air mixture and causes the engine to run. On the other hand, a diesel engine is a compression combustion engine that doesn’t require a spark. The air mixture explodes on its own due to the force of the compression.
Why Do Diesel Engines Need Diesel Exhaust Fluid?
After the 2008 mandate, the EPA issued even stricter guidelines in 2010. Diesel engines had to reduce their NOx production, so the DEF additive reduces this emission. Heavy machinery and diesel trucks can only operate within these guidelines by adding DEF fluid.
This is why you’ll find heavy-duty diesel trucks manufactured after 2010 with a diesel fuel tank and a Diesel Exhaust Fuel tank.
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How Often Do You Need to Fill Up the DEF Tank?
It all depends on your mileage as the def consumption matches the fuel consumption. You will use more if you are towing vs operating empty. Each truck is different, but light-duty trucks generally consume 2 or 3 gallons of DEF per 800 miles. The DEF tank is usually 7 to 10 gallons. Most manufacturers have installed an indicator of some kind on diesel trucks to alert the driver of low DEF.
Medium and heavy-duty trucks use more DEF. Generally, for every 50 gallons of diesel fuel, the truck burns 1 gallon of DEF. For example, if a heavy-duty truck drives approximately 120,000 miles a year, the DEF tank will be refilled about 20 times.
Where Can You Get Diesel Exhaust Fluid?
One of the best places to get DEF is at truck stops. You can’t go to any fuel center and expect to find it. Love’s, Flying J, Petro, and Pilot Travel Centers are all good options. The greatest advantage to filling up at these locations is you can fill up with fuel and DEF on the same trip.
- One gallon of is used approximately every 300 miles
- A truck with a 20 gallon DEF tank can go up to 6000 miles between...
- When used in an SCR system will reduce the levels of NOx...
You can also purchase DEF at retail stores like Walmart, Target, O’Reilly’s Auto Parts, and Advance Auto Parts. But DEF is a substance you must be careful handling if you’re not using a pump at a truck stop.
How Do You Identify a DEF Filling Pump From a Diesel Fuel Pump?
DEF pumps are usually beside diesel pumps at truck stops. The nozzle is very skinny and much smaller than the diesel nozzle. There is a black flap or covering that holds the DEF nozzle in colder climates. The cord on a DEF nozzle is usually on a reel instead of loosely hanging from the pump like the diesel fuel cord.
The diesel pump at truck stops is normally green or black, while the DEF pump is usually blue (but don’t always trust the colors). Make sure to always read the label before pumping.
What Are the Cons of a DEF Truck?
The biggest con of a DEF truck is the hassle of keeping an eye on the DEF tank and refilling it as needed. In the early generations of DEF systems, there were a lot of failures as well. DEF head failures are common and sometimes the systems can cause reliability issues for the vehicle. In general DEF systems have become much more reliable in newer generation systems and the biggest drawback is just having to purchase another fluid for your vehicle.
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What Happens to the Engine If the DEF Tank Is Empty?
Most times your vehicle will continue to operate without DEF but at a very limited power level. You may not even be able to drive the speed limit. If you let it go too long the engine may shut down completely and not restart. Its also possible to end up damaging the exhaust system if you let the DEF run out.
Always pay attention to the gauge or sensor that monitors the DEF level.
Is All DEF Fluid the Same?
There are 12 major manufacturers of DEF. All of these manufacturers should be following rigid guidelines set by the EPA. This means there should be no difference between brands. All Diesel Exhaust Fluid should contain 67.5% distilled or deionized water and 32.5% high-grade pharmaceutical urea.
If you’re looking at a cheaper off-brand, you just want to make sure it is EPA-approved and check if it’s gone through testing. This will be on the bottle if you’re purchasing DEF from a retail store.
Take Care of Your Diesel Engine by Understanding Diesel Exhaust Fluid
For your diesel truck to have a long life, proper maintenance is key. Replacing the air filters, changing the oil, and adding DEF are all part of taking care of a diesel truck. If you take care of your diesel engine, it could last twice as long as its gas engine counterparts.
So what is Diesel Exhaust Fluid? A critical component to your diesel engine truck!
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