replenishing the fluid themselves.
The worst thing that can happen
to an SCR system is being filled with
contaminated or incorrect fluid. This
can potentially cause thousands of
dollars in damage to the emissions
system and leave drivers stranded.
What can also leave drivers with a
thumb out by the side of the road
is running the DEF tank dry. The
EPA requires vehicle manufacturers
have measures in place to ensure
equipped vehicles cannot run without
Vehicle manufacturers all handle
this in slightly different ways. Some
employ the use of a gauge, while
some have a simple warning light.
Generally speaking, however, when
the DEF tank level drops below 10
percent, a warning of some kind will
be displayed on the dash, indicating
it’s time to fill up.
The warnings will get progressively
more frequent, brighter, or louder as
the level continues to decrease. If the
vehicle is allowed to run out of fluid,
one of two things will happen: either
engine power will be cut and speed
limited to essentially a “limp-mode,”
or the vehicle will not start until the
fluid is replenished.
wrong tank, be sure to insert the
DEF nozzle into the truck’s DEF
inlet to avoid contaminating the
5. Store DEF below 86 degrees (F)
to maintain its optimal shelf life.
6. Do not store DEF in direct sunlight.
7. Do not refill previously used
DEF containers, as they may be
Keep Drivers in the Loop
It’s also important for drivers to
know how long DEF will last them
and where they can find it if they start
to run low. On average, 2. 5 gallons
of DEF yields about 350 miles. That
means, as a rule of thumb, drivers
should refill their DEF tank every
third time they fill their diesel tank.
In addition to using on-board
GPS navigation systems to find the
nearest DEF retailer while out on the
road, some DEF manufacturers have
made smart phone apps that can
identify the DEF retail outlet closest
to a driver’s location.
These apps can be very helpful as
they allow users to search for DEF
retailers by city, state and zip code,
view a map with the various DEF
refueling locations along their route
and find the addresses of nearby
Although these tips and guidelines
for getting the most out of DEF aren’t
widely known, adhering to them isn’t
difficult. By purchasing the right
amount of DEF, ordering it from
a reliable supplier and educating
colleagues about handling, storing,
using and finding DEF, users will be
able to maximize their fleet’s fuel
and cost savings.
In modern truck engines,
DEF is critical
Emissions regulations have been
on the minds of over-the-road drivers
for some time now. It began with
the implementation of exhaust gas
recirculation (EGR) systems, then
progressed to the diesel particulate
filter (DPF), and now the buzz is around
selective catalytic reduction (SCR).
SCR systems use a consumable
diesel exhaust fluid (DEF) in
conjunction with a catalyst to reduce
nitrous oxide (NOx) emissions.
Because the fluid is consumed during
the system’s normal operation, it
requires the vehicles owner to not
only monitor the fluids level but also
refill it when it’s been used up. Here is
some useful information on the fluid
that truck operators need to buy.
SCR technology uses ammonia to
break down NOx emissions produced
during diesel combustion into
nitrogen and water. SCR has become
the technology of choice for a majority
of truck and engine manufacturers
to meet the stringent 2010 emissions
standards set by the EPA for heavy-duty trucks.
The biggest benefit of SCR for the
vehicle owner is in the fuel savings the
technology provides. Because SCR
deals with NOx outside the engine,
manufacturers are once again able
to tune their engines to run more
efficiently and produce more power.
The increase in engine efficiency also
leads to a reduction in particulate
matter, resulting in less frequent
regeneration of the DPF and adding to
the increased fuel economy.
SCR works by first routing exhaust
gases through an oxidation catalyst,
which removes hydrocarbons and
converts a small amount of NOx
to NO2. The next step requires an
injection of an aqueous urea solution,
DEF, into the exhaust stream at a
precise dosing rate. Exhaust fluid
is converted into ammonia, which
reacts with the remaining NOx in the
SCR catalyst to produce harmless
nitrogen and water. A final catalyst is
sometimes installed downstream of
the SCR catalyst, which is designed to
remove any remaining ammonia from
the vehicle’s exhaust.
DEF is a mixture of synthetic,
high-purity urea and deionized
water. This liquid is clear, nontoxic,
nonflammable, non-explosive, and
generally nonhazardous. Additionally,
DEF is classified as a minimum
risk for transportation. The fluid
is mixed at a ratio of 32.5 percent
formaldehyde-free low biuret urea
and 67.5 percent deionized water.
Heavier than diesel, exhaust fluid
weighs 9. 1 pounds per gallon, and
while it will freeze at 12 degrees,
its composition and quality are not
affected by freeze or thaw.
It is recommended that exhaust
fluid be stored between 40 and 80
degrees, and it has an effective shelf
life of one year when stored at 80
degrees. Prolonged storage above
86 degrees will cause hydrolysis to
occur. The most important quality of
diesel exhaust fluid is its purity. For
example, one teaspoon of salt would
contaminate 5,000 gallons of DEF.
SCR systems are very sensitive
to potential impurities, so it is
essential that exhaust fluid remain
uncontaminated, and that consumers
only purchase fluids that adhere to
the ISO 22241 quality standard and
never try to mix their own. In Europe,
the German Association of the
Automotive Industry (VDA) controls
the “AdBlue” trademark and uses it
to ensure DEF quality standards are
maintained in accordance with DIN
70070, which is similar to the United
States’ ISO 22241.
Do It Yourself
One of the biggest complaints
about the use of SCR is the fact that
eventually you are going to run out of
exhaust fluid. Refilling your vehicle’s
DEF tank is a whole lot easier than
the dealer might make it seem.
As of now, BlueDEF brand exhaust
fluid is available at most truck stops
across the country, making it easy
to locate, and new brands and retail
outlets are popping up constantly. Since
DEF is nontoxic, virtually anybody
can refill his or her vehicle simply by
purchasing the proper amount of fluid
and locating the fill port, usually next
to the fuel filler, under the hood, or in
the trunk if it’s a diesel-powered car or
SUV that needs filling.
People can potentially save
hundreds of dollars by simply