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BMW 5-Series (G30) Forum Mechanical Maintenance - Break-in, Oil, Fluids, Servicing 2018 M550i 91 vs 94 Octane

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      06-15-2021, 09:41 PM   #1
akashkotecha
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2018 M550i 91 vs 94 Octane

Hey all,

I was wondering if anyone can provide input on whether the octane level will make any sort of difference in the cars performance.

I was told that the car has been programmed to run on 91 octane and therefore using 94 octane will make no difference unless the car is tuned to run on 94. Is this true?

I used to spend extra and get 94 octane but now I only refuel with Shell 91 here in Canada as thats one of the few options that does not have ethanol in it. The 94 octane fuel does have ethanol which I was also told is not best for these engines.
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      06-15-2021, 10:19 PM   #2
Superjackson
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94 will maybe run slightly cooler but you will get less mileage because of the ethanol. No tune, no power difference. Stick to 91 unless you tune.
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      06-18-2021, 05:07 PM   #3
430Scud
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I would use whichever is less expensive. As mentioned you will get little benefit from 94, and ethanol (up to 10%) is only a problem if the car sits for weeks or months. That is because the ethanol can separate, and straight ethanol can be damaging to rubber and plastic components in fuel pumps, lines, etc. But as long as it is in suspension in normal use, no problem.

In WA State, ethanol free gas is difficult to find, but I drive all my cars regularly. My friends with collector cars will seek out ethanol free gas for the benefit in rarely driven cars. (they use a fuel stabilizer as well)
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      06-23-2021, 02:19 PM   #4
Bill BMW OR
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My suggestion is to see if "clear" premium is available in your area. No ethanol at all. I notice a small difference in performance running clear 92 octane with a MPG boost as well.
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