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Diesel Exhaust Fluid (DEF) in Telehandlers

Blog Posts - Jan 19

Diesel Exhaust Fluid (DEF) in Telehandlers

JLG Industries, Inc.
World-leading access equipment manufacturer
McConnellsburg, PA

The introduction of Tier IV Final  / Stage 4 engines to many telehandlers with the most recent emissions regulations brought along with it the addition of diesel exhaust fluid (DEF), which is a vital part of the exhaust emissions strategy of selective catalytic reduction (SCR).

Most industrial engine manufacturers developed their complex engine emissions technology strategies over the past decade, delaying the introduction of DEF to the extent possible for aerial and construction equipment such as telehandlers.  Cost of the DEF technology in addition to standard operating cost, space claim, maintenance, system troubleshooting complexity along with operator training and awareness are all factors OEMs and end users associate with this type of system.

On the most basic level, the SCR system causes a chemical reaction in the exhaust stream of a diesel engine to reduce the nitrogen oxide emissions (NOX) released through the tailpipe of the vehicle.  Generally, systems are composed of an SCR exhaust aftertreatment device or ‘can’ in the exhaust stream to which a DEF injector device is attached. A tank holding the DEF fluid and pump to transfer the fluid to the injector round out the system.   The DEF is injected into the exhaust stream of the engine where the chemical reaction occurs to reduce the NOX.


So what exactly is DEF?

DEF is a mixture of roughly one third urea and two thirds purified water. It is an additional fluid that must be maintained in regular maintenance of the vehicle.  It is generally housed in a tank near the fuel tank of the vehicle and is usually only a fraction of the fuel tank volume.  For most systems, the DEF tank volume must last longer than the fuel tank volume, and multiple fuel tank fills can occur before the DEF tank volume needs replenished.

OK, adding SCR / DEF to a vehicle sounds straightforward and users shouldn’t sweat it, right?  Well, there are some things equipment owners and operators need to know, because this isn’t a system that can be ignored or abused without potential repercussions as they relate to vehicle downtime and maintenance costs.

This isn't a system that can be ignored or abused without potential repercussions as they relate to vehicle downtime and maintenance costs.


What you need to know about DEF.

Keep. It. Clean. Always use only quality DEF fluid and keep it clean.  The system must be able to detect when an inferior or incorrect fluid is introduced to the DEF tank.  Even trace amounts of a wrong fluid (like diesel or wiper fluid) can trigger a problem with the system and put the engine in a derated condition until corrected.  Often an entire system cleaning is needed to correct the mistake.  Keep dispensers and any funnels used clean and dedicated only to DEF.


DEF can become stale in storage.  Shelf life of sealed containers of DEF are generally much longer than DEF that remains in the tank of a vehicle sitting idle for an extended period.  Fluid left in a vehicle without replenishment and/or use may experience some water evaporation, changing the concentration of the fluid.  General recommendations are to check DEF fluid concentration using a refractometer after two or more months of vehicle inactivity.


DEF will freeze.  Since DEF is 2/3 water, the solution will freeze when the vehicle is not in use and temperatures approach 12 degrees F.  But don’t worry, the system is designed to recover from a frozen tank.  Coolant from the engine is circulated in a coil immersed in the DEF tank to return and to help keep the solution a liquid - generally within an hour after starting.  During this thawing time, the vehicle can be utilized as it normally would be (as long as it is allowed to remain running).  Since DEF will freeze, vehicles also have a specific shutdown sequence that must be allowed to complete before battery disconnect switches are activated.  To prevent DEF from freezing inside the hoses between the tank, injector and pump, the DEF pump will continue to run for approximately 45 seconds after the engine has been turned off to allow it to purge the lines of fluid.  While the engine is running, these hoses are heated to prevent the fluid within from freezing.


Keep DEF at appropriate fill levels.  If DEF level in the tank is allowed to become too low for too long, the engine system will progressively warn the operator and eventually derate itself until the vehicle becomes inoperable.

Maintain the DEF system.  While it doesn’t require a lot of routine maintenance beyond fluid level replenishment, like any fluid system, there are some periodic maintenance points.  Some DEF tanks have a filler neck screen – remove and clean this when any debris is noticed.  DEF tanks have a suction screen where the DEF fluid is drawn out of the tank to the DEF pump – follow maintenance guidelines for replacement in the operator manual.  DEF pump units also have a filter cartridge – follow maintenance guidelines for replacement in the operator manual.  Finally, some systems also require a maintenance regeneration after an extended period of engine operation to remove any DEF crystallization that may have accumulated at the DEF injector within the exhaust system.  Regeneration is a process where the vehicle must be left inoperable with the engine running for a short period of time (generally 30-60 minutes).  During this period, the engine may automatically run at elevated speeds to increase exhaust system temperatures to levels needed to clean the DEF system – consult the vehicle operator manual.

Smart operation is important. How you operate the vehicle may affect the SCR / DEF system.  As with any exhaust aftertreatment system, adequate exhaust temperatures are periodically required to keep the system operating optimally and efficiently.  Avoid continuous short interval start / stops of the engine that don’t allow the exhaust system temperature to stabilize.

SCR / DEF systems are a vital part of meeting today’s stringent emissions regulations for all heavy equipment including telehandlers.  Although they may seem intimidating at first, when understood and properly maintained, these systems become just ‘another component’ of the vehicle. Whatever your application, you can trust that JLG has various after-treatment and engine options to meet changing Tier IV regulations and emissions standards while also providing you with the options you need to get the job done.


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