I've run filtered waste peanut oil from my turkey deep fryer in my old 300SD. Usually about 1 gallon per tank or so. Never had a problem.

I do this only as this is a better way to dispose of the old oil than putting it in the trash.

I probably go through about 10 gallons of oil a year, and using the waste oil as fuel offsets some of the cost of the oil initially.

I think I get about 5 gallons (labeled 35 lbs) for about $22-$25.
So it's about $4-$5/gal. when new. If I can use it later in my fuel tank, I'm saving about $1.5/gal, which helps somewhat.

Of course, I couldn't do this in the winter, as the oil would solidify. It's strictly a summertime deal. Then again, I don't use my deep fryer much in the winter, as it's too cold to be outside messing with it. :)

I'm tempted to run the waste peanut oil in my recently acquired 92 300D 2.5 turbo, but haven't done it yet. Maybe I'll throw a gallon of oil it it tomorrow, as I'm heading to Chicago and will blow through that tank quickly.

Chris