Biodiesel works fine in older cars, but can create problems when first used in them. That’s because biodiesel is a solvent that cleans diesel engines, fuel lines, and fuel tanks, loosening the gook that may have accumulated in them from petroleum diesel, especially in the fuel tank. This material then flows into the fuel lines and through the fuel filter, where it can obstruct the flow of fuel.
But as I just said, that doesn’t mean you can’t use biodiesel in an older car.
Not at all; you just have to start slowly.
In order to use biodiesel in an older vehicle, you should start with a blend of biodiesel and regular diesel — around 10 to 20 percent biodiesel, for instance. Run the car on this for a while, being sure to change fuel filters frequently until the tank and fuel lines are cleaned.
Next, increase the concentration of biodiesel blend a bit more. Continue to change the fuel filter until you are sure that the gunk has been purged. When the fuel tank and fuel lines are clean, you can then switch to 100 percent biodiesel. If your vehicle is older than 1995, you may have to replace the rubber seals and fuel lines with a synthetic material, Viton, that is resistant to biodiesel.