Although I've run darned little D2 in either of my MBs, I've never noticed any noticable difference in milage between D2 and bio. I've read that bio gets about 90% of what D2 gets, but I honestly think my cars do as well or slightly better on bio.

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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