Use 89-octane gasoline (Plus) in Cooper S?

[Unambiguous]

This post is US-centric.

Since I bought my 2003 Cooper S (British Racing Green, black top) in May last year, I have filled it with super unleaded as recommended in the manual. But lately gasoline prices have been getting to me. While I get quite decent milage (27 mpg around town, 33-34 highway), I can't get used to paying $2.20 - $2.30 / gal. for 93-octane. So I have been using 89-octane for the last few months. As far as I can see or hear, there has been no downside to this: the engine never knocks, it doesn't strain audibly on hills or when passing at speed, it seems as responsive as ever, and the milage I have been getting seems to be unchanged. I live on the US east coast and have never driven the car above an altitude of 3000 feet; your results may vary in mountain country.

Does anybody know for sure if it's safe to use 89-octane in a Cooper S? I know what the manual says. What are the risks?

[bd394]

Quote: Originally Posted by Unambiguous

This post is US-centric.

Since I bought my 2003 Cooper S (British Racing Green, black top) in May last year, I have filled it with super unleaded as recommended in the manual. But lately gasoline prices have been getting to me. While I get quite decent milage (27 mpg around town, 33-34 highway), I can't get used to paying $2.20 - $2.30 / gal. for 93-octane. So I have been using 89-octane for the last few months. As far as I can see or hear, there has been no downside to this: the engine never knocks, it doesn't strain audibly on hills or when passing at speed, it seems as responsive as ever, and the milage I have been getting seems to be unchanged. I live on the US east coast and have never driven the car above an altitude of 3000 feet; your results may vary in mountain country.

Does anybody know for sure if it's safe to use 89-octane in a Cooper S? I know what the manual says. What are the risks?

I do not believe there are any risks at all. The engine is designed with knock sensors to detect even the slightest detonation (knocking) before its gets bad enough to hear it. In this way the engine can run without risk. Although, there will be some less noticable effects because of the spark adjustment made by the computer such as less power and gas mileage. It may be difficult to notice these things though.

[Purple Haze]

I think it's worth the extra two bucks per fill up for peice of mind.

*shrug*

[Humourl3ss]

No offense, but if the price of (still relatively cheap American) gas is making you think twice about using the manufacturer specified octane rating, you really might perhaps want to consider a different car that uses 87 as a matter of course.

Or failing that, concentrate on your driving and maintenance habits first (lessening the amount of hard acceleration you use, keeping tires at proper inflation, making a greater effort to plan trips to avoid unnecessary driving or congestion, etc).

Downgrading one's choice of octane should be the absolute dead last option.

-CW

[EBMCS03]

Seriously... how much more does it cost to use 93? vs 89? You save like $2 a tank! Like Humourl3ss said if you cannot afford to fill up the car with proper gas or is worried about that 1 dang mpg you bought the wrong car. Go get a Prius or a Insight even a Corolla or somthing... 27MPG in city driving and 33 MPG in highway???!?!?!??! WHAT MORE do you want?

[onasled]

Not to jump on the ban-wagon here , ...BUt man, what are you thinking?
You need to think about why in fact you bought an S rather then just an MC.
Come on now .... Just put the right gas in it or trade it in for the MC

[Z1GZAG N]

Quote: Originally Posted by onasled

Not to jump on the ban-wagon here , ...BUt man, what are you thinking?
You need to think about why in fact you bought an S rather then just an MC.
Come on now .... Just put the right gas in it or trade it in for the MC

For those who drive the S and don't know, the MC in the US requires 91-93 octane also.

But like the rest have said, 89 is only a buck cheaper per tank. Even if you fill up three times a week, you're only talking $156.00 a year to operate the MCS on the fuel it was designed to use.

Besides, it make conversation at the pump. People see me filling up with Premium and just have to ask why I don't use 87. I tell them it's a performance car meant to me hot rodded.

[sequence]

here it's about 8 cents difference between 87 (our mid-grade here in the Rockies) and 91 octane, so it's a no brainer. I run my 1986 carbed Toyota PU on mid-grade, and my MCS on high grade. A P66 station close to me knocks 6 cents off premium UL every tues and fri so I plan my gas trips around that (last it was 1.95/gal w/the discount.)

Now, I have heard that for those folks who have difficulty cold starting their MCS's (a common problem) that lower octane fuel will help (lower flash point than premium.) I think this instance is the only time I'd be tempted to use lower octane gas. Jimbo

[snek]

Why are people getting so upset, calling the guy cheap and irresponsible if there are no side effects?

[Ryephile]

I believe the Siemens EMS2000 is mapped to handle 91 to 99 RON, so it can probably handle 89 R+N/2. That said, you will lose some power. It just math, not magic. The MINI, and especially the MCS, was never designed to be a penny-pincher at the pump. You're obviously not driving your car hard (track, etc.) otherwise you would be getting the highest unleaded octane you can find price-no-object

Buy what you want, [shrug]

[Dave]

Let's apply a little logic to the question:

1. Why does the S "require" 91 octane

Because the engine runs at a higher effective compression under boost. The higher the compression the higher the octane to achieve the performance that a higher compression yields.

2. Can you use a lower octane?

Yes - most likely this will NOT hurt your engine. Unlike older generation vehicles that did not have engine control electronics that monitor the ignition timing and adjust as necessary, the MINI will automatically retard the timing to avoid pinging and potential engine damage. For around town driving at low rpm the boost is, in fact, low enough that the effective compression works just fine with a lower octane gasoline.

3. Am I saving money?

If your engine were a naturally aspirated (not supercharged) engine running at a high compression ratio this would be a very simple question to answer. And the answer would be NO. By retarding the timing the engine runs less efficiently, effectively lowering your fuel economy to spare your engine from serious damage.

BUT you're driving a supercharged engine - so IF you drive it like a little old lady, seldom getting above 3000 rpm then it's possible that you would save a penny or two - maybe.

Would I run 89 octane gas in my MINI? Only if there was no alternative and then just enough to get me to the next gas station.

Hope this makes sense,


Dave

[Z1GZAG N]

Quote: Originally Posted by snek

Why are people getting so upset, calling the guy cheap and irresponsible if there are no side effects?

It's because there are side effects!

I guarantee BMW would not set the required octane rating at 91-93 if it were not required. They have to know some potential buyers are going to walk when they see this requirement.

Refusing to run premium fuel when required by the manufacturer is as bad as the person that buys a Hummer and then complains about the fuel mileage.

[MINIAC]

Quote: Originally Posted by Unambiguous

I can't get used to paying $2.20 - $2.30 / gal. for 93-octane.

I'd wish I only had to pay that much for premium gas ... 91 octane is over $2.70 here

[EBMCS03]

Quote: Originally Posted by snek

Why are people getting so upset, calling the guy cheap and irresponsible if there are no side effects?

How you know there are no side effects? Have you ran two MINIs for X amount of years one with 87 and one with 91+ and can scientifically prove that there was no difference? I dont buy that. I'm sure there are side effects. Heres one story... My dad had a Celica GTS and he ran premium for a while and switched it over to 87 for a little less than a year and the car ran much worse... less power, less smooth. Ok you migh argue that the MINI now has plenty of sensors to prevent all that but in the end something isnt running optimally on what it was designed to run on. You knew what the car needed before you bought it.

[bodinski]

Why are so many folks' shorts in a knot?I use mid-grade sometimes, super others. No problems. No pinging. I think it'd ping on regular, though. If they suggested mid-grade, we'd try regular. THEN, there'd likely be trouble.
Don't sweat it...