April 18, 2021
DEF is now required for many diesel engines to reduce emissions. Using DEF is simple when you understand the facts.
Diesel Exhaust Fluid (“DEF”, also “AdBlue”) is a liquid used to reduce diesel engine pollution.
Specifically, DEF is an urea solution made with 32.5% urea and 67.5% deionized water. DEF is
integrated into the exhaust system through the selective catalytic reduction (SCR), which
lowers the concentration of nitrogen oxides (NOx) in the diesel exhaust emissions from a diesel engine.
DEF is stored in its own fluid container, and it is sprayed into the exhaust stream by an
advanced injection system and then converted into ammonia on a special catalyst. Most larger
diesel engines are required to meet emissions standards (Tier IV on off-highway vehicles).
DEF fluid is consumed at a rate of between 2% and 6% relative to diesel fuel, depending on the
Emissions regulations in most developed countries now require some sort of after-treatment solution
to reduce diesel emissions. DEF fluid is one of the most cost effective and cleanest ways to
meet these regulatory guidelines.
13 Bullet Points On Diesel Exhaust Fluid
#1 What is DEF?
DEF is a mixture that contains 67.5% deionized water and 32.5% urea. When introduced into the
hot exhaust gas, the water in DEF gets evaporated naturally, and it leaves behind
ammonia and isocyanic acid. These two compounds help clean diesel exhaust.
#2 How often should the DEF tank be filled up?
You should always check your DEF fluid levels and refill the same way you do with your
diesel fuel. DEF is consumed at a slower pace than diesel, however, the tank is also much
smaller. Timing to refill your DEF fluid depends on the relative size of your DEF and diesel
tanks, as well as your engine specifications (some engines use more DEF than others). As a precaution,
always travel with extra DEF fluid and fill it whenever the level gets to about a quarter full.
Your engine may not run or could get damaged if your DEF fluid is empty.
#3 Where can I buy DEF?
DEF is widely available at most truck centers and service stations. It is also available
at big box retailers such as Wal-Mart. It is typically sold in large jugs.
#4 What are the advantages and disadvantages of using DEF?
DEF engines are much cleaner burning, however they come with a higher price tag given the
extra components required. There really is not a choice — most engines in developed countries
are required to have integrated emissions treatment solutions, and DEF is the cheapest and
most effective way to meet guidelines.
Not all countries in the world require the use of DEF. As a result, often the export
markets prefer non-SCR engines because they are cheaper to operation and maintain.
#5 Does DEF lower fuel mileage?
No. DEF trucks that come with the SCR technology are inbuilt with a smog control feature
that gives better fuel mileage to your truck. According to experts, DEF trucks have at
least 5 to 7% better fuel mileage than the other trucks.
#6 Is DEF technology proven?
Yes, DEF technology has been used for many years now — in agriculture, power generation and
other industrial applications. Urea, when blended with heat, can reduce NOx by 70% or more.
While the nitrogen-based fertilizers used in agriculture are of less purity,
the automotive-grade urea used in industries is of very high purity.
#7 Does DEF evaporate when not used for awhile?
Yes, but it can take a long time for the DEF to evaporate. At about 125 degrees Fahrenheit, DEF,
if not used, would take around two years to turn into ammonia and evaporate. However, you can
expect some evaporation even at 86 degrees Fahrenheit because DEF contains almost 67% of water.
#8 Is DEF toxic?
Urea is mostly used in fertilizers and cosmetic products. While it doesn’t cause any fatal
diseases, urea can cause some allergies to the eyes, skin and respiratory system.
When you ingest urea in very high quantities, it can turn toxic for you.
#9 What happens to the engine if the DEF tank is empty?
The DEF tank should be treated just like the normal fuel tank in a vehicle.
When this tank is empty, your engine will not run or fail to start.
Today, it is mandatory for all diesel engine manufacturers to include a warning system
located on the dashboard so the driver knows the DEF fluid level.
#10 Does DEF freeze?
At 12 degrees Fahrenheit, the 32.5% DEF solution starts to crystallize.
DEF is comprised of water which will naturally freeze. DEF will expand when it
freezes, the same way ice cubes expand in the freezer.
#11 How should I store DEF?
The DEF container in your engine typically has a system to address frozen DEF fluid.
You should be mindful of extra DEF containers you keep on hand — try to store them
in areas without large temperature fluctuations.
#12 How regulated is the production of DEF? Can I produce it on my own?
No, consumers cannot and should not make their own DEF. DEF contains additional
additives. Using the wrong fluids can damage your engine or SCR.
#13 What is the shelf life of DEF?
At stable room temperature the expected shelf life of DEF is about two years. Hotter
climates reduce the shelf life to one year or shorter.