I get about 24 also (mostly town, some highway) running b100. I've read that bio doesn't produce as much power or get as good milage --- I once ran a tank of ULS diesel just to see. Besides lots more engine noise, my milage dropped about 10%.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln