Why do you want to do this. There are many good lubricity additives that are designed to be used with diesel fuel. Putting a quart of veggie really does nothing except maybe make you feel better?

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1981 300D 147k
1998 VW Jetta Tdi 320k
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1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair