Answers to Some Frequently Asked Questions About Diesel Exhaust Fluid

DEF, short for diesel exhaust fluid, is a non-toxic solution composed of urea and de-ionized water. When sprayed into the exhaust stream of diesel trucks, it breaks down the harmful NOx emissions produced by burning this type of fuel into nitrogen and water. The system used to prevent dangerous emissions from being released into the atmosphere is called a Selective Catalytic Reduction system, often referred to simply as an SCR.

Just about all commercial trucks fabricated from 2010 on feature SCR systems, as do many pickups and SUVs. Those who drive vehicles that require DEF might want to read on to find out more about this product and its use. Answers to some of the most commonly asked questions about DEF can be found below.

How Much is Required?

DEF consumption can be measured as a ratio of fluid to fuel use. This ratio is generally referred to as the dosing rate or the treat rate, with medium to heavy-duty trucks typically featuring a dosing rate of between two and three percent. What that means is that approximately two to three gallons of DEF will be required for every hundred gallons of diesel fuel the truck consumes.

What Happens if it Runs Out?

The EPA requires truck manufacturers to utilize measures that ensure that their vehicles can’t operate without DEF. Typically trucks display a series of alerts on their dashboards when their DEF is running low. If the tank runs completely dry, the vehicle’s speed will be limited to five mph until it is refilled.

How Does SCR Affect Vehicle Performance?

Since SCR is an after-treatment technology, it does not adapt combustion conditions within the engine. As a result, it has actually allowed truck manufacturers to improve their vehicles’ fuel efficiency and increase their torque. In comparison, the alternative to SCR, referred to as Exhaust Gas Recirculation, functions by reducing combustion temperatures, which can negatively impact performance.

What Happens When Drivers Spill DEF?

There’s no need for protective clothing when handling DEF since it is non-toxic. It can, however, wind up staining clothes and will turn into white crystals if it is allowed to dry before cleanup. Any small amount of spilled DEF can be simply washed away with water.