I've been adding strained, used, Peanut oil off & on since Dec. Not more than about a gallon per tank ful, & I think it acturally runs better when I'm using it. It's diluted with the diesel fuel enough it hasn't gelled yet with temps a little above zero at times, but I'm using regular fuel additives also. I had a bunch of the used oil to get rid of, so I just started putting it in the tank at fill ups, a little bit at a time. Cheaper than buying the kit. I poured it through cheese cloth, and every other fillup, open the drain a little on the fuel filter to drain out anything that might have settled to the bottom of the housing. I'm out of warranty at 153k, but it's been doing fine.