Merlo Tech Talk: DEF and the Overfill BluesApplied Machinery Sales
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.
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.