I run 91-94 Octane. On a conservatively tuned Twincharged. I will never put in anything lower than 91. I also have used a few gallons of C-16 mixed with the premium fuel. I have no catalytic converter and I routinely check my spark plugs. Never had an issue.

 

If you had lived somewhere that actually has a winter season, you would be able to run a lower octane during that time because the air is cold enough to support it.
The Cooper has a pretty decent compression ratio, so I wouldn't run anything less than the mid grade where you live.
If at all possible, you should run a Top Tier gas...
http://www.toptiergas.com/

 

Seriously, at a 10 cent difference, and filling maybe 10 gallons at a fill, it is the difference of $1. If you fill once ever 4 days, that's a difference of $91 over the year and $910 over 10 years (life of the vehicle?). I consider that cheap insurance.

 

 

I'd be careful about that. There have been a few MINI owners who have had fuel system problems from using gas with too much ethanol in it. I suggest reading what the owners manual says is ok & sticking with that. I don't remember off hand how much ethanol is ok.

http://www.michiganmini.org/forum/in...p?topic=2945.0

 

My '03 Cooper seems to run a bit better on 89 octane mid-grade than on premium. Also, I see no reason why 87 octane would be a problem. If the mileage is lower, (and it may not be), it's likely to be less than the amount needed to make up for the cost difference between regular and premium.

 

All premium, all the time.

 

Is it worth saving 3 bucks per tank not to use premium? No...

 

I've found that when I use premium when it's crazy cold (30 and below) it starts really nasty(wanting to die at idle). But when I use a mid grade it's not affected by the cold. Anybody else have this issue?

 

My mini failed to start then did a nasty start during the seasons first cold snap. Then I had a bout of what sounded like engine knock at 10°F. Other than those two isolated instances, no real problems.

I run 93 year-round.

 

I think some of the octane enhancers they use can cause this, I've heard a few others talk about the same problem. Just because it cost more and they call it "premium" doesn't mean it's always better.

 

Yes, I have heard even Mini recommend the mid grade for cold seasons for people experiencing these cold start problems.