What is DEF?
Diesel Exhaust Fluid (DEF) is a 32.5% aqueous solution of high-purity urea (ammonia) in demineralized water. DEF is utilized by the selective catalytic reduction (SCR) system to reduce the nitrogen oxide (NOx) emissions from diesel engines. DEF is a non-hazardous substance and is not a fuel or fuel additive. Vehicles equipped with an SCR system will have a separate reservoir with a separate filling cap for adding DEF. DEF should never be added directly to the diesel tank.
Facts about DEF:
- DEF is composed of 32.5% urea and 67.5% demineralized water
- Consumption of DEF is estimated to be 2% of fuel consumption
- DEF is non-toxic, non-polluting, and non-flammable
- DEF may have a slight odor similar to ammonia
- DEF will freeze at 12°F but is not harmed by freezing and is usable once thawed
- Exposure to extreme heat and direct sunlight while in storage could degrade the DEF
- Studies by engine manufacturers have shown a 5% increase in fuel economy using the SCR system
- Maintenance, durability and performance of diesel vehicles is not affected by the SCR system