Merlo Tech Talk: DEF and the Overfill Blues

Merlo Tech Talk: DEF and the Overfill Blues


The DEF tank placement is readily noticeable by its blue cap, found on the Merlo telehandler in or near the engine compartment.

When the DEF fluid flows through the injectors uninhibited, it works in complete synergy with the machine’s exhaust system and the Diesel Particle Filter (DPF). When a blockage occurs, the fluid cannot reach the exhaust system, and engine performance will decrease exponentially.


DEF and what it does

Diesel Exhaust Fluid — a mixture of urea (usually synthetic) and deionized water — is sprayed into the exhaust system to break down the generated NOx from the diesel fuel into harmless nitrogen and water molecules.

On the Merlo telehandler, DEF refills are not as frequent as adding diesel fuel. The DEF gauge, located on the LED on the steering column, will indicates DEF levels.  Merlo tech manuals suggest refilling the DEF tank at recommended maintenance interval (hours: 500/1000/1500).


Filling the DEF tank

Simply put: Do not fill beyond the top of the tank itself. Unscrew the blue cap. Looking inside and see the place where the ‘neck’ joins the tank. In most Merlo’s this place of joining has a flap in place. Do Not fill beyond this connection.

The neck of the tank acts as a breather tube for  DEF. If it is “capped off” by overfilling, the DEF within the tube crystalizes. Crystalized DEF prevents air from entering the tank. This means the pump can’t move the fluid out of the tank and do its job of breaking down the NOx.  Habitual capping off chokes engine performance. Plus, when temps dip to zero and below overfilled DEF could freeze causing blockage.


Diesel Particle Filter Sensors

When the DEF cannot be pulled into the injectors, the emissions sensors inside the Diesel Particle Filter (DPF) send a signal to the machine’s computer.  Just as in a car or truck, a symbol will illuminate on the dash. If action is not taken to rectify the issue, the sensors increase their presence by switching from a steady light, to a flashing light, to a flashing light with intermittent sound.


This chart shows the progression of operator notifications from correct functionality- Level 0 and Level 1 only—to full stop of functionality.

Available for download here.


When you see the light

Levels 1 and 2:

  • Perform a requested regeneration
  • Perform an automatic regeneration

Regeneration capabilities depend on the model and motor for that model.

For those units with requested regeneration:

  • STOP, but DO NOT turn off the machine
  • Press the appropriate button located on the dash cluster
  • Take a break, and let the unit cycle through.

Levels 3, 4 and 5 are when the machine needs to be immediately stopped.

At this juncture you will need to contact your local Merlo dealer or AMS-Merlo technical support.


If the unit does not have requested regeneration, please contact a local Merlo Dealer. Or contact the AMS-Merlo Technical Advisors as to the next steps by calling 803-327-4949 or sending an email to:  service@appliedmach.com

Share this post


    Find a Dealer

    Fill out this form, and we will put you in touch directly with your local Merlo dealer and service provider.

    AgricultureConstruction

      Become A Dealer

        INQUIRE ABOUT RENTALS

        Delivery Address

        Get a Quote

          GET A QUOTE

          Delivery/Pickup Location

          BuyRentRe-RentNot Sure
          AgricultureCement MixerCompactConstructionMaterial HandlingRoto