Accidentally Used Unleaded Instead of Diesel

You may be able to tell the difference between diesel and unleaded fuel, but your boat’s engine can’t. It will try to burn whatever you put in the tank, but won’t get very far. If the dock attendant fueled your boat with the wrong fuel, the fuel dock may clean up the whole mess – if you’re a local and a regular customer. Otherwise, you’re probably on your own.

  1. From Tank to -- Oops

    • If you catch the mistake quickly, and before the engine is run, the problem is limited to the tank. If it’s a removable tank, you simply disconnect the fuel hose and set the tank out of the boat. If it’s a built-in tank, the problem is a bit stickier. You’ll have to find someone to de-fuel the tank. The dock operator may do this. If not, waste operators in your area may pump the fuel. If you’re a dedicated do-it-yourselfer, there are pumps, both electric and those with a foot-pedal, to pump the tank out.

    From Tank to Pump

    • If you ran the engine for more than a few minutes, the problem may be a bit deeper. Once the tank is de-fueled, it’s time to turn your attention to the engine, specifically the fuel filters, fuel pump, and fuel rail and injectors. You'll need to disconnect the fuel lines from the tank to the primary and secondary fuel filters, as well as the line to the pump. You'll need to replace the two primary fuel cores and fill the bowl with diesel fuel.

    Pumps and Fuel Injection

    • You need to remove and empty the fuel line between the low-pressure fuel pump and the fuel rail. Drain the primary fuel filter/wager separator by removing the separator bowl crank the engine. Follow the fuel line to the fuel rail. You may consider removing the injectors and the fuel rail and clean them in a solvent, but unleaded gas is fairly strong as solvents go. Remove and disassemble the rails and the injectors if you feel more comfortable doing it. While the parts are soaking, you can reinstall the fuel lines and return the separator bowl to the fuel filter/water separator.

    The Final Touch

    • Finally, you're in the home stretch. You can reassemble the fuel pump and make the appropriate fuel line connections to the fuel pump and fuel rail. After you make the final connections it's time to install the injectors and connect the fuel rail to remove the last, lingering vestiges of gasoline from your boat's diesel engine. Fill the fuel tank with diesel fuel. You can add a bottle of biocide if it comforts you. Refiners put biocide in the fuel before it leaves the refinery. If you worry that the fuel will pick up microbes between the refinery and the tank, ask yourself why you don't add biocide to your gasoline-fueled car.