If you are brave, and take issue with mfg recommendation, do what I did in my cheaper days: Run through three tanks of each octane, always from the same station. Drive the same with each tankful. Measure MPG for each one. If MPG drops consistently on a lower rated fuel, then the car is kicking back timing - it NEEDS the higher octane. You will probably break even, or possibly save, by running the correct (more expensive) fuel. You have a nice car, that wasn't cheap. Don't cheap out here.

 

Had an occasion to stop by the dealer last night. Brought up the whole octane question and here is what both my MA and the sales manager had to say -- the "S" will run just fine on 89 octane. (Look inside the gas door) Won't do any harm to the O2 sensor or any other engine parts. Depending upon what brand gas you buy you should add a fuel system cleaner containing Techron every couple thousand miles.

When I asked him why the gas door says 89 and the manual says 91 his response was, "I have no idea. We've been told at company sponsored training events to tell customers that 89 octane is just fine."

I'll probably trade up to a JCW in a few years so longevity isn't an issue for me.

 

My guess is because there is a difference between "acceptable/just fine" and "recommended", but most people speaking the English language don't understand that.

 

The 2012 manual actually just recommends (not highly), but now its recommending 93 for JCWs. We don't get 93 in part of the world.

 

Right out of the 2011 CM Manual (pg 113) In a non S you can use 87 under most conditions. In an S you need to use a minimum of 89 but when the difference is 10cents a gallon I would most definitely use 91.

Required fuel
Super Premium gasoline/AKI 91
This gasoline is highly recommended.
However, you may also use gasoline with less
AKI. The minimum AKI Rating is:
[FONT=Calibri]> [/FONT]Cooper S: 89
[FONT=Calibri]> [/FONT]Cooper: 87
If you use gasoline with this minimum AKI Rating,
the engine may produce knocking sounds
when starting at high outside temperatures. This
has no effect on the engine life.
Do not use any gasoline below the specified
minimum fuel grade. Otherwise, the
engine could be damaged.[FONT=Calibri]<[/FONT]
Use high-quality brands
Field experience has indicated significant differences
in fuel quality: volatility, composition,
additives, etc., among gasolines offered for sale
in the United States and Canada. Fuels containing
up to and including 10% ethanol or other
oxygenates with up to 2.8% oxygen by weight,
that is, 15% MTBE or 3% methanol plus an
equivalent amount of cosolvent, will not void
the applicable warranties with respect to defects
in materials or workmanship.
The use of poor-quality fuels may result in
drivability, starting and stalling problems
especially under certain environmental conditions
such as high ambient temperature and
high altitude.
Should you encounter drivability problems
which you suspect could be related to the fuel
you are using, we recommend that you respond
by switching to a recognized high-quality brand
such as gasoline that is advertised as Top Tier
Detergent Gasoline.
Failure to comply with these recommendations
may also result in unscheduled maintenance

 

Funny, we don't get 91 around here. It's either 87, 89 or 93 at almost every gas station.

 

Betty has been fed a diet of 87 with no problems. When it gets hot (over 90) she gets premium.

 

Finally, someone who know's what they're talking about in this thread. Concur entirely with Mr. Luckypa.

My 2005 was fed 92 BP for it's first 3 years, and 87 for the past 3 years mostly from Quik-Trip with virtually no difference in performance. About the only noticable difference occurs in the summer. If going uphill on an interstate entrance ramp with the air conditioner on, there is an ever so slight noticable performance improvement burning the premium gas.

The rest of the time it's a complete waste of money. And with gasohol being added to fuel everywhere anyway, any concerns you might have about fuel system components being affected by lower octane gas are totally eclipsed by the alcohol being dumped in your tank. Not to worry though, the drought is going to fix that. By spring there won't be anyone adding alcohol to gas. And with a pound of ground beef running about $16 a pound a year from now, a lot of folks with any sanity will realize that the money wasted on premium gas can be spent on far more satisfying endevours like a $13.50 one pound package of bacon.

 

But you have a "Justa" right? 87 in a Justa is fine. Maybe not so in an "S"

 

I wish we had Top Tier 94 octane fuel that is Ethanol-Free in the West Coast.

 

I don't know much about Minis as this is my 1st time owning one but when I 1st bought my Cooper S I was putting 87 in, the car was making a knocking noise and I called the dealership to task, the 1st question was what kind of fuel are u putting in. I switched to 93 and the noise went away. I did notice a slight difference in performance too.

 

Wow...I can't believe you put 87 in!


Anyways, I always put 93 Shell brand only.

 

The cars are EPA tested with 91, hence the statement on the gas filler door. Per MINIUSA via email, 91 is not required with acceptable minimums of 89 for turbos and 87 for normally aspirated second gen cars.

However, by alternating 89 and 91 fillups over ten thousand miles I verified that running 89 in my base Cooper gets slightly poorer mileage which negates the ten cents per gallon savings at the pump. YMMV.