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Old 07-13-2008, 05:15 PM
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JCL JCL is offline
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Agree with others on the expected mileage, that is why SUV prices have dropped so quickly.

As to premium fuel, you can try to save money but you may in fact not do so. You don't actually need 91 AKI, you need fuel that doesn't pre-ignite in your driving conditions. If the octane is too low, the engine will retard the timing. You will not harm the engine. If the timing is retarded due to pre-ignition, you will likely get reduced mileage, negating any advantage to not buying premium.

Now, the trick is figuring out what your fuel is actually like locally. Fuel varies widely in quality and octane rating (AKI) across the US. Premium is spec'd because it covers all the bases for BMW. If you like, try a tank or three of lower octane fuel. Measure the mileage. If it drops, then that is a good sign that you need the premium that your local station is selling. If it doesn't drop, that is a good indication that you can keep on using it. I would go to 89, not 87. If all this is too much trouble, just use 91.
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