Originally Posted by LugNut
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?
Oh, I know. There's no production car out there that runs straight ethanol. Maybe some experimental ones, but nothing you can buy from Ford or the like. Either way, E85 would be sure to ruin your engine. I don't think the Germans have even considered ethanol as a fuel source.
Like someone else said, I doubt it's a low octane that you bought. Almost any new car with computer-controlled timing can retard the engine to allow for the use of lower octane gas. You won't get as good of mileage and it
might hurt the engine, or at least put some stress on it, but it won't knock. Not for long at least.
The bad gas was most likely high in water content. Again, gas treatment may help with the problem. Most of those little bottles like octane boosters and fuel system cleaners are made of petroleum distillates, something of which your engine has no problem lighting on fire. So they might be better than gas-line antifreeze. They usually include some other chemicals for their purposes that your engine can burn.
Either way, the answer is still 10%. I can guarantee using anymore than that will damage your engine.