When Should I Change My Diesel Exhaust Fluid? - Foster Fuels

How Long Does Diesel Exhaust Fluid (DEF) Last?

Diesel exhaust fluid normally has a shelf life of about two years. However, exposure to sunlight or sustained high temperatures can compromise it. Any DEF purchased at a truck stop or auto parts store will have a clearly labeled expiry date — using DEF past this date can cause performance issues and potential maintenance problems.

How To Calculate DEF Requirements

All newer diesel vehicles have a dashboard warning system that alerts you when it’s time to change your DEF. To estimate how much you’ll need, you’ll need to know the efficiency of your engine.

DEF is consumed at a rate of about 2-3% relative to the amount of fuel you are using. This means between 1.2 and 2.0 gallons of DEF will be required for a vehicle with a 65-gallon gas tank. If you have a five-gallon DEF tank, DEF should be replaced every third or fourth time you fill up. However, the easiest way to avoid a problem is simply to top off periodically.

What Are DEF Hazards

Because DEF is mostly water, there is a risk that it can evaporate or freeze. Evaporation occurs at high temperatures, but preventing it is easy — simply keep unused DEF in a tightly closed container. Within the tank itself, there is no risk of contamination.

DEF can freeze at temperatures below 12°F. However, manufacturers have included a number of safeguards to prevent damage when this occurs. Trucks can still be run normally with frozen DEF — most tanks feature heating elements that will automatically warm it over the course of normal operation.

DEF that has been previously frozen won’t be compromised. Water and urea freeze at the same rate, so the basic ratio won’t be affected. However, frozen DEF does expand, typically by about 7%. To prevent damage to your SCR system in cold weather, give fluids a minute to drain back into the tank before shutting down your vehicle’s battery.

For more information on how to keep your SCR performing optimally, contact us today.

Learn More About Diesel Fuel

• How Long Does Diesel Fuel Last?
• How Do I Check My Diesel Exhaust Fluid Level?