The higher octane fuel affords a bit better mileage BECAUSE of it's resistance to preignition. not having to compensate (more foot) for lost energy transfer due to a poorly timed mixture ignition = mileage!

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RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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