My girlfriend recently bought a 2009 Mini Cooper (regular model, not the S). The manual says that she should use premium gas. I tell her it’s not necessary and she’s just wasting her money. She’s been listening to me and the car runs fine. Her parents keep telling her that she should follow the instruction manual and use premium gas because it will affect the longevity of the engine. Is this correct? Can we keep using regular gas? If not, what affect will it have on the car, if any?
Thanks,
Paul
She should follow the owner’s manual. If she didn’t want to pay for premium gas she shouldn’t have bought a car that requires it. The Mini is a performance car (even the base model) and requires premium fuel for correct operation.
You’re not going to save her any money in the long run.
Her parents are correct. She should be putting premium gasoline in her Mini.
Does the manual say “required” or “recommended”? If “required” use premium. If “recommended”, regular gas should be ok. My wife’s 06 Toyota Sienna “recommends” premium gas for additional performance, we’ve used regular since new with no issues.
Ed B.
The answer is really unknown. It depends on specifics of engine and driving style/conditions etc.
I agree that only premium gasoline should be used. The secretary in my department bought a MiniCooper and loves the car. She uses premium gas and claims that the mileage on the Mini is so much better than the Ford Probe that she owned that her gasoline bill is much less even though she used regular in the Probe. Perhaps the OP should get a regular gas girlfriend the next time around.
The cost to use premium is not as bad as some might think. If we assume that there is no effect on gas mileage, then it will cost about $114 for each 10,000 miles to use premium rather than regular. If we assume just a 10% decrease in mileage, the difference drops to $13 - basically no difference. I’d just use premium. BMW determined that the car runs best with premium gasoline, and I believe it is best to follow the manufacturer’s - the expert’s - recommendations.
Thanks everyone for the feedback. We will use premium gas from now on.
Paul
The difference between “regular” & “premium” is 5 octane points, 87-92…In my opinion, no engine ever suffered damage because of a lack of 5 octane…Engines will tolerate a LITTLE spark knock indefinitely, an annoyance perhaps, but not a destructive force. If you can not detect any audible detonation with your EARS, you are NOT damaging the engine…
A better test might be fuel mileage and performance. If you can see a noticeable improvment in either, then MAYBE premium fuel offers a worthwhile advantage…
And it can’t have anything to do with the fact that the Probe may just get less miles per gallon?
The Probe did get less mpg. The point is that the mileage is so much better on the Mini than on the Probe that the overall gasoline bill is less even though the Mini uses premium.
The base Cooper also has something like a 10 gallon tank(S model has 13 IIRC), so it’ll take very little to fill it up. My Civic has an 11.9 tank, and even at $4/gallon, I never spent $40 to fill it up.
I read a technical article that said that knocking/pinging is one of the most destructive things you can do to your motor.
It also said you should only run premium fuel if you are hearing knocking/pinging. Most modern engines will detect pinging and retard the timing to prevent the pinging from occurring.
Additionally, if you live at higher elevations, lower octanes perform like higher octane fuels since octane is merely a measure of resistance to burn and at higher elevations, there is less oxygen in the air and automatically the fuel is going to be more reluctant to burn.
All that said, I only run premium fuels in my high performance/high compression engines. As another poster said, the cost is negligible and the increase in mileage can offset that cost anyway. I had an old Nissan pickup that would get so much better mileage on premium that it was actually cheaper to run premium than regular, but your mileage may vary. 
dp