Best advice I can give is to look carefully at the pump every time you fill up. I was getting fuel from the local Hess station regularly. The pump had the Ultra Low Sulfur sticker on it. One day as I am standing there waiting for it to fill I look at the pump and it has a new sticker on it. It said it contained some percentage of Bio-diesel. Too late. It was already in. Wasn't long before warning lights started showing up. Took it to the dealer and they said that stuff didn't even smell like diesel fuel. By then I had run most of it out. So a new fuel filter went in and the rest got diluted with good diesel.