Best Practices

Diesel Exhaust Fluid


Operator Tips

When to refill the tank

  • On CASE equipment, there is a DEF gauge, just like the fuel gauge. It shows the fluid level and indicates when it's time to refill.
  • When fluid level becomes low in the DEF tank, a series of warnings will alert the operator after DEF reaches less than 10% of capacity.
  • If the DEF tank contains less than 5% of its capacity, the equipment engine power will de-rate. Enough power will be available, however, to travel a short distance, so you can add DEF to the tank.
  • The DEF tank needs to be filled once every 3 to 4 times that you refuel with diesel fuel in CASE machines. The frequency will vary with operating conditions.

How to fill the tank

  • The opening of the DEF tank is sized to accept only a DEF fill nozzle. This constraint ensures that only DEF can be pumped into the DEF tank. A standard nozzle for diesel fuel will not fit into the DEF tank opening.
  • DEF tanks will hold between 15 and 50 gallons, depending on the equipment size and horsepower.

Don’t trap DEF in hoses

  • After you shut down your equipment, wait 60 seconds before turning off the battery. The delay allows any remaining fluid to drain out of the hoses, back into the tank, lowering the likelihood of damage from DEF freezing.
About DEF

Diesel Exhaust Fluid (DEF) is non-toxic and is made up of purified water and urea. It is stable and colorless. DEF is similar to baking soda in its alkalinity (pH). It is not a fuel but is used to reduce the level of nitrogen oxides in the emissions to meet emissions control standards.

In the Selective Catalytic Reduction (SCR) system, DEF is injected into the exhaust. It converts the NOx into nitrogen gas and water vapor, which are harmless components of air.

Keep your DEF in a temperature controlled, dry environment away from direct sunlight. If you can’t store your DEF indoors, cover your tanks with heat blankets in cold weather to reduce the possibility of freezing. DEF will freeze at 12°F when not in use and will 'slush' before then. The DEF tank on the vehicle has a heater that will thaw the DEF quickly. Freezing and thawing does not change its effectiveness.