Quote:
Originally Posted by dyzfnctional
I was flipping through the manual on my 435i and noticed that the minimum fuel grade it suggested is octane 89, should i just go with premium or maybe do every other fill of 89 and 91? Any thoughts?
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I'm sure this topic gets beaten to death around here. The short answer to your question, use as low of an octane as you can without getting any knock (knock is where the fuel combusts before it is supposed to).
Running fuel that is too high in octane is actually bad for the engine since it can burn too slowly, contrary to popular belief, high octane gas isn't "cleaner" and it won't get you better mileage (using octane higher than what the engine was designed for actually decreases mileage), it just burns slower which some engines (such as forced induction engines) require.
So if BMW suggests a minimum of 89...I'd use 89. If my 335i requires a minimum of 89, I'd just put 89 in it. It isn't because I want to save the money (the marginal savings is nice though I suppose) but because that means 89 is the most efficient fuel to use for the motor.