Do’s and Don’ts for Using Diesel Exhaust Fluid


When the Environmental Protection Agency required all diesel-powered 2010 and later light-duty vehicles sold in the U.S. meet stricter emissions standards for oxides of nitrogen and particulates, most vehicle manufacturers added a selective catalytic reduction (SCR) system as an after-treatment rather than re-designing the diesel engine itself.

The key to lowering NOx and particulate emissions in diesels comes with the injection of diesel exhaust fluid (DEF) into the exhaust stream. By turning NOx into simple nitrogen and water vapor in the exhaust, manufacturers can focus on improving performance and engine efficiency while limiting owner diesel maintenance of the exhaust to adding DEF to the separate DEF tank and monitoring the regen cycle.

Proven Technology

A combination of two-thirds deionized water and one-third urea, DEF is based on emissions reduction technology that has been used power generation and agricultural products for a half-century. However, diesel equipment manufacturer, Volvo, advises of a few issues that DEF users should be aware of.

Contaminated or low-quality DEF can cause several problems, most of which are expensive to repair and may void the vehicle warranty. Most often, bad DEF can result in poisoned catalyst and deposits that build-up on injectors or filters. Look for a label that indicates the DEF complies with the API’s voluntary certification program.

DEF Do’s

  • Keep it clean. DEF is easily contaminated by airborne particles or residue in storage containers. Contaminated DEF will degrade SCR system performance and possibly damage the engine. Keep the fill nozzle area clean.
  • Store the fluid in DEF-only containers, either stainless steel or HDEP plastic jugs.
  • Store in a cool, dry place in an expandable container and out of direct sunlight; recommended temperature range is 12 – 86 degrees F (-11 – 30 degrees C). Below 12 degrees F, DEF will turn slushy but can still be used.
  • Test DEF quality with a digital refractometer. Urea concentration range is 32.5 – 37%.
  • Top off the DEF tank daily if possible to avoid condensation.

DEF Don’ts

  • Confuse the DEF and diesel fuel fill caps. If filled incorrectly, stop the engine immediately and contact a service professional.
  • Store DEF in metal containers made of carbon steel, aluminum, copper or zinc. DEF is not toxic but it will corrode certain metals.
  • Ever add de-icer fluids to DEF.
  • Use DEF that has been stored for longer than one year.
  • Run the diesel engine on an empty DEF tank. The engine will run without DEF but performance will be de-rated and eventually, the engine will not start until DEF is added.