I just got a Mini S. Without knowing what kind of fuel it had in the tank from the dealership, when I went to a gas station for a refill, I got Premiun (93 octane in Florida) as I read in the label the the suggested was 91 or higher. Since then, and after only two weeks of sweet magic motoring since I got it, I started getting knocking and noise from the exhaust pipe. Could it be that the car previously had mid-range fuel loaded (and the engine pre-tuned for it) and then with the mix with a different higher octane fuel, these type of reactions can happen? Is that normal? Should I just go back to mid-range, or just keep on loading premium and expect the car to eventually get adjusted to it and stabilized by itself?

 

Man, there is a lot of talk about this around. I actually spoke to my MA about it, and he told me to try 89 octane. Around here, it is either 93 or 89. There is no place near me selling 91. I was not having knocking with the 93 ( I have a 2003 Cooper). I was having a very, very intermitent problem with low idle/stalling occasionally after the engine was initially started and I drove approximately 150 yards to the stop sign in the parking lot at work. My MA quickly suggested trying 89 octane. I am almost through the first full tank, and I have noticed no performance or mileage difference with the 89 vs. 93. Maybe you could go back to 89 and see if that stops the knocking? I think it is worth a shot. But I don't think the car should be knocking due to too much octane. If I were you, I'd take the car to the dealer.

 

Try using the same brand all the time. I have settled on Mobil and it is available most everywhere. The premium seems to produce consistant
results and mileage is 29 mpg. and if I could keep my foot out of it,
maybe better.

 

Too much octane won't hurt a thing. Too little is not good for the engine and is generally false economy because you get less power from the engine and worse MPG. It's worth the extra buck every fill-up to use high test.

 

I agree with petecrosby. Too much octane won’t hurt. If you want to economize and meet the 91 octane requirement, you can mix mid-range and premium. Locally mid-range is 89 octane and premium in 93 octane. So half mid-range and half 93 octane should give you approximately 91 octane. (Be sure to take a few quick corners for good mixing.) You mention a knocking noise from the exhaust pipe. Is it possible that this not engine knock, but an exhaust problem?