What is DEF made from?

DEF is a mixture of deionized water and a mixture of synthetic automotive grade urea. It's carefully regulated by the American Petroleum Institute.

Do I have to fill the DEF tank with each fill-up?

No, depending on how much you're hauling, the rate of DEF use is about 2.5 gallons for 800 or so miles of travel. Depending on what year and model truck you have, you could have a fuel-gauge-like readout, a digital indicator or a simple "low" light.

Where can you buy DEF?

As you might expect, truck stops are likely to carry several brands of DEF, sometimes in multi-gallon containers or available at the pump. Here are just a few places we've found that carry DEF: Walmart, TravelCenters of America, Flying J Truck Stops, Love's Travel Stops, Petro Stopping Centers, and Pilot Travel Centers. Plus, you can purchase it by the gallon at many auto parts stores like Napa Auto Parts and Advance Auto.

There are more cons than pros with a DEF-equipped truck.

The only cons we can find are that the trucks cost a bit more, DEF requires some room in your truck, and it adds a nominal amount of weight. The pros include more optimized combustion, better fuel efficiency, increased power, reduced maintenance, fewer regenerations, less wear on the engine, plus it yields harmless nitrogen and water into the atmosphere, and it's highly reliable.

NOx isn't a big deal in the first place.

NOx is an element in exhaust that has been blamed for acid rain, smog and raising the overall greenhouse gas levels of the planet. DEF, as part of a SCR (Selective Catalyst Reduction) system, turns NOx into harmless nitrogen gas and water (which is present in the air we breathe). Whether you believe these man-made chemicals have a role to play in climate change or not, NOx is something we don't need to spew into the environment.

Are there weather limitations consumers should be aware of?

The shelf life of DEF is directly related to the temperature in which it is stored in. Storage temperatures between 12 and 86 degrees Fahrenheit are recommended to maintain optimal shelf life of up to 2 years.DEF does freeze at temperatures below 12 degrees Fahrenheit, but a vehicles heating system will melt DEF so it is completely safe to operate these systems in freezing temperatures. At a constant 120 degrees it would take two years for the DEF to turn into ammonia and evaporate. You can stop worrying about evaporation of DEF.

DEF will kill my fuel mileage.

Quite the contrary. Because the manufacturer is able to tune the engine any way it wants to, and then allow the SCR and DEF to take care of the pollutants, most manufacturers have discovered better fuel mileage (compared to other smog-reduction systems). Truck manufacturers claim it improves fuel mileage by as much as 5 percent.

Is DEF prone to contamination?

Yes. SCR systems are extremely sensitive to chemical impurities in the urea solution. Just one teaspoon of salt can contaminate 5,000 gallons of DEF. Purity is critical to ensuring proper function.

Is DEF safe to handle?

DEF is non-hazardous and non-toxic, non-flammable and non-explosive. Urea is the active ingredient in DEF, and it is used in fertilizers, plastics, animal feed, pharmaceutical applications and some cleaning agents. DEF is less toxic than many other fluids in a truck, including diesel fuel, engine oil, brake fluid, antifreeze and windshield washing fluid.