Quote:
Originally Posted by elfhearse
I think the minimum recommended octane level is 91.... Personally. I would never go below 91 octane. Finding a 91 or 93 octane no ethanol is usually limited to gas stations that are near lakes , bays to service the marinas. ( marine engines hate ethanol. )
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Correct. The manual says that you should not use lower than 89, but 91 is recommended.
They don't recommend 91 just to get you to part with money. When using 89, the engine will adjust to avoid knocking by delaying the ignition, which causes less complete combustion, and higher gas usage. So while it runs fine on 89, what you save at the pump, you lose most of by getting worse mpg.
Lower octane can cause more engine wear and earlier wear-out of the catalytic converter, which is why BMW recommends 91.
There's not much point in going much above 91, though.
93 is fine, but won't work better than 91 for normal driving. Above that is not recommended unless you have a tuned car and preferably changed intakes too.