2008 Duramax manual says bio 5% max. How safe to use up to 20% on the rare occasion when I can't find any 0-5% and near empty?
If you already did it then you'll soon know. If you haven't, carry a few 5 gallons jerry cans of #2.
I would not use the 20 percent, just use standard pump diesel like BohoMark stated.
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