Diesel Exhaust Fluid (DEF) is a vital component of a Select Catalytic Reduction (SCR) system. It’s a clear solution made of Urea and water that’s colorless but has the smell of ammonia. When added to the system, it enters the exhaust stream, where it breaks down Nitrogen Oxide emissions into Nitrogen gas and water vapor – two basic components of the air we breathe. Your machine has a separate DEF tank that varies in size depending on what model you’re running, and it usually has a blue cap for easy identification.
The DEF tank is for DEF, not diesel. The diesel tank is for diesel, not DEF.
If you put diesel into a DEF tank, diesel is less dense than DEF so that it will float on the DEF. If diesel enters the SCR catalyst, significant damage can occur that may require servicing or a costly replacement of the catalyst. If you put DEF into a diesel tank, the diesel becomes contaminated because DEF is composed of urea and water. If the equipment is started, introducing the diesel/DEF mixture into the engine, you’ll end up with longer term consequences. If the DEF is introduced to a diesel storage tank, the DEF will, if not removed, cause damage to the fuel system. DEF is corrosive and harmful to many metals.