Thanks, but actually E85 means 85% ethanol, 15% gasoline (but more gas than that in winter to help with cold-starting). Ethanol has a higher octane rating than gasoline, something like 105 if I'm remembering correctly. But a lower heating value, so lower mileage.

Those expensive little bottles of gas-line antifreeze are mostly, if not only, ethanol. So E85 is a much cheaper source.

I'm not looking to run straight E85, just to add some to raise the octane. What's the highest percent ethanol that the XFs can handle?