Best Practices

Diesel Exhaust Fluid

Diesel exhaust fluid (DEF) has quickly become a necessity on every jobsite. Formulated to reduce vehicle emissions, the fluid works by treating exhaust gases after they have left the engine. With the importance of DEF fluid projected to increase, follow these tips on proper use to get the most out of your equipment.

About DEF


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


In the Selective Catalytic Reduction (SCR) system, DEF is injected into the exhaust. It converts the NO2 into nitrogen gas and water vapor, which are harmless components of air.


The ideal temperature range for storing DEF is between 32°F and 86°F, and its average shelf life is 3 years. Keep DEF out of direct sunlight and do not store it in temperatures below 32°F. Because of its alkalinity, DEF fluid can cause oxidization in the same way that oxygen rusts raw steel, so it needs to be stored in plastic or stainless steel containers.

What to know when filling your DEF tank

DEF tanks are designed so that the opening will only accept a DEF fill nozzle. A standard nozzle for diesel fuel will not fit into the DEF tank opening. This safeguard ensures that only the proper fluid can be pumped into the tank. DEF tanks will hold between 15 and 50 gallons, depending on the size and horsepower of your equipment. Be sure to keep enough reserves on hand, as equipment will cease to operate once the DEF tank is dry.

When to refill the tank

A DEF gauge has been added to most new equipment that will show the fluid level and indicate when it is time to refill. When the DEF fluid level reaches less than 10% capacity, a series of warnings will alert the operator. 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 that you can add more fluid to the tank. The DEF tank needs to be filled once for every 3 to 4 times that you refuel with diesel fuel. The frequency will vary with operating conditions.
Contact Heavy Machines today for more information on diesel exhaust fluid.