It's interesting that my 500SEL gets 10% lower mileage on 10% ethanol gas. Soooooo the ethanol does nothing in my car. On a 2000 mile trip I would use 111 gal of 10% ethanol gas. Same 2000 miles on non ethanol gas I would use 100 gal. The eleven gal of ethanol just goes out the tail pipe only stopping long enough to corrode or damage something and INCREASE the emissions.
I still can't explain the 20 mpg using Exxon and Sta-bil.

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84 500 SEL (307,xxx miles)