Putting DEF in the Diesel Tank: What Happens and What It Costs
Putting DEF into the main diesel fuel tank — not the DEF reservoir — is a costly mistake that is becoming more common as more DEF-equipped vehicles enter the NZ fleet.
The Rising Frequency of DEF Misfuels
As DEF (Diesel Exhaust Fluid) becomes standard on modern diesel vehicles in New Zealand, a new category of misfuel is emerging: drivers filling the main diesel fuel tank with DEF, or filling the DEF reservoir with diesel. Both are damaging, but DEF in the diesel tank is the more serious scenario by a significant margin.
What DEF Does to a Diesel Fuel System
DEF is a 32.5% solution of urea in deionised water. It is highly corrosive to metals used in diesel fuel system components — particularly the copper and aluminium alloys used in fuel pump internals and injector bodies. Within minutes of DEF contacting a diesel fuel system, corrosion begins. If the engine is started with DEF in the fuel tank, the high-pressure pump will begin to fail almost immediately, and the corrosive mixture will be circulated through every fuel system component.
The Cost
DEF in the diesel tank almost always requires replacement of the fuel pump and injectors — the most expensive components in a modern diesel engine. Typical repair costs for this scenario in New Zealand range from itemised charges on our rate card to significant cost depending on the vehicle. Do not start the engine. Call EEK Mechanical on (866) 777-3712 immediately.
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