What's Up With My Exhaust Fluid?

What’s Up With My Exhaust Fluid?

DEF tank

Diesel Exhaust Fluid (DEF) plays a critical role in meeting emission compliance requirements. But if any common vehicle fluids (including water) are accidentally added to the DEF tank, the Diesel Exhaust Fluid will be contaminated, leading to damage of system components and making the emission reduction properties of the system ineffective.

Some ways that contaminated DEF can be detected include the following:

  • DEF is usually clear, but when it comes into contact with copper or brass it will appear “light blue,” and if it comes into contact with steel or galvanized steel, it will appear to be a “rusty” color.
  • DEF is heavier than diesel fuel and oil, so these fluids will float on top of the DEF.
  • It has a slight ammonia smell.

If you suspect that the DEF has been contaminated but are unable to confirm by smell or color, you should test the fluid using a refractometer, or on some vehicles a DEF quality test can be run using a scan tool.

About the Author

Chris Manescu

Chris Manescu joined the Mitchell 1 Commercial Vehicle Group as a Technical Editor in 2010. Chris worked as an ASE certified repair technician for over 20 years after his service in the United States Marine Corps.