Premium Gas and Mini Coopers

May 20, 2005 6:27 PM

Do Mini Coopers really need high-octane gas? (Apologies to my boyfriend for asking this question because he says they do! I'm just not convinced.)
posted by abbyladybug to travel & transportation (35 comments total)

Your use of 'gas' implies you're in the US, but if you're in, say, Western Europe.. then no. If you're in the US, it's more likely, due to lower quality gasoline. I would imagine a Google search could bring up a more decisive answer quickly.
posted by wackybrit at 7:16 PM on May 20, 2005

Mini says yes, yet my sister who has a Mini has yet to use anything but 87 octane (regular) and hasn't had any issues.
posted by karmaville at 7:25 PM on May 20, 2005

depends on the person you ask and the year of the mini cooper. I've been told to use high octane in my '64 chevy because 1) the engine is old, and 2) they used higher octane gas back then and 3) it's easier for the engine to break it down.

now, supposedly, in newer cars, they burn regular unleaded more/as efficiently as premium, because the timing automatically adjusts in order to run on regular. This, i think, is conventional wisdom. However, I have a friend who still believes in running high-octane in his late model volvo is best because he's of the opinion that, yes, the timing adjustment WILL make it run efficiently on lower octane gas, but that the adjustment will reduce the performance/power of the car.

is he right? I don't know. i'm sure someone will come along with an educated answer.
posted by fishfucker at 7:27 PM on May 20, 2005

Well, here's an excerpt from this AAA article.

Detonation that goes unchecked for even a very short time will create extreme pressures and temperatures in the combustion chamber.
These conditions will quickly burn holes in pistons, damage valves and cause other severe engine damage that will cost thousands to fix. Also consider that if your vehicle is under warranty when these type problems occur, the manufacturer will not cover the repairs if it is found that the required grade of fuel has not been used. So, before you choose to save 20 cents per gallon by purchasing regular-grade fuel rather than premium, be sure to ask yourself, "Is the benefit worth the risk?" For the vast majority of drivers the answer will be "No."
posted by aaronh at 7:32 PM on May 20, 2005

"For the vast majority of drivers"

Meaning people whose auto manufacturers recommend higher-octane gas. Not the vast majority of ALL drivers.

Do you guys have an owners manual to check? It should say something inside. If this is just an academic conversation you're having at home.... :)
posted by scarabic at 7:41 PM on May 20, 2005

According to the manual, the 2005 mini requires 91 octane unleaded gasoline. Using lower octane gas isn't recommended.
posted by mosch at 7:57 PM on May 20, 2005

If it starts "pinging", switch to high octane. Otherwise, check your owner's manual.
posted by Eideteker at 8:01 PM on May 20, 2005

I wonder if they got a tax break for offering this "feature" on their cars?
posted by idontlikewords at 8:21 PM on May 20, 2005

My mechanic brother says to always use the lowest grade possible. If you have problems with it, step up.
posted by schustafa at 8:33 PM on May 20, 2005

The short version.

1) If it pings, you need more octane. If it pings on 93, you need work done to the car.

2) Measure your mileage. Try the next higher octane grade. If you mileage improves, do it again (might be a fluke.) If it stays improved, then your engine was retarding the spark to avoid detonation in the combustion chamber, and you were hurting your mileage. If it doesn't improve, the higher octane gas is a waste of money.
posted by eriko at 8:37 PM on May 20, 2005

The 2004 Mini Cooper S uses a fuel injector and the manual says to use only premium gasoline.
posted by aaronh at 8:39 PM on May 20, 2005

I wonder if they got a tax break for offering this "feature" on their cars?

What, a high-compression engine? It's the nature of a smaller high-revving engine to require gas that won't prematurely explode - namely, high octane.
posted by thedevildancedlightly at 9:27 PM on May 20, 2005

Do what the manual says. If the manual asks for 91 octane, use that as a minimum. If it asks for 87, then 87 is fine. If you use less, you won't notice any obvious problems, but the computer will retard the ignition timing (to prevent detonation or "pinging") and you will have poor performance and worse emissions because of it. In other words, just follow the owner's manual!
posted by knave at 9:31 PM on May 20, 2005

What if it asks for 87 and you put in 93? Are you going to burn up your engine?
posted by mecran01 at 11:06 PM on May 20, 2005

mecran01: no, you'll just throw money away and build up carbon faster inside the engine, which will eventually require you to throw even more money away.

Just use what octane the owner's manual recommends. Going higher is usually pointless; going lower is usually not a good idea long-term.
posted by pmurray63 at 11:22 PM on May 20, 2005

My ex girlfriend's father, who was an exec at Ford: "Never buy high octane gas. It's a sham."

My step-father, who owns gas stations/a gas distributor: "Never buy high octane gas. It's a sham."

Those are two people I'd tend to believe. Now that I've heard the same from Schustafa's brother...
posted by incessant at 11:26 PM on May 20, 2005

To add another possible case, on some engines, automakers may say that regular 87 (US) is acceptable, but midgrade 89 is preferred. In a case like this, the only downside may be less power. But if it says premium 91 required, believe it.

Again, just follow the owner's manual recommendations.
posted by pmurray63 at 11:26 PM on May 20, 2005

Just for reference, I asked a similar question exactly one year ago to the day.
posted by Tallguy at 6:52 AM on May 21, 2005

Click and Clack from Cartalk say follow the manufacturer's recommendation.
posted by wsg at 7:48 AM on May 21, 2005

The owner's manual definitely says to use high octane. I just don't trust corporations, even if it isn't Exxon making the car... I just don't buy it.
posted by abbyladybug at 9:02 AM on May 21, 2005

It may be worth mentioning that in Germany "regular" is 91 octane. (And I don't recall seeing lower than 95 here in the UK.)
posted by cell at 9:55 AM on May 21, 2005

cell, octane is measured differently in Europe and the US, hence the higher numbers.

abbyladybug, the auto manufacturer is *not* lying. High compression and forced induction (turbo or supercharged) engines often need high octane gas. The 2005 Cooper S has a 10.6:1 compression ratio, which is definitely aggressive.
posted by knave at 10:29 AM on May 21, 2005

My bad... the Cooper (not S) has a 10.6:1 compression ratio. The Cooper S is supercharged and has an 8.3:1 compression ratio to allow for the boost from the supercharger. It doesn't surprise me that either model would need high octane.
posted by knave at 10:32 AM on May 21, 2005

And here's a good article about what octane means to you.
posted by knave at 10:34 AM on May 21, 2005

High-octane gas: What’s the point?
Millions of vehicles suggest it, but is it worth the price? [NBC Nightly News | May 20, 2005]
posted by ericb at 11:01 AM on May 21, 2005

Also worth noting, octane requirements change with altitude. If you are in Denver, Salt Lake, or someplace else >4000 feet, the regular grade is probably 85, rather than 87, so if you move to a similar elevation with a car that specifies 87 octane gas, get 85 octane regular and skip the higher test. The same holds for scaling down the higher grades.
posted by Good Brain at 11:10 AM on May 21, 2005

Just want to add the chorus of "Use what the car manufacturer recommends." They're not trying to get you to buy a new car sooner, and they're not subsidizing the oil industry. Those specs are created by engineers to preserve their reliability numbers. Higher octane is just going to hurt your wallet, but lower octane can lead to all kinds of (expensive) problems in the future. As in, the after-your-warranty-is-up future.
posted by Civil_Disobedient at 11:10 AM on May 21, 2005

I tried a tankful of 87 in my 2004 Cooper. She pinged alot
So I only use 91 now.
posted by CCK at 11:38 AM on May 21, 2005

Good points, Knave and Civil Disobedient.

Another way to look at it is cost. Figure driving 15,000 miles a year at 30 mpg. That's essentially filling up 10 gallons every week. If regular is $2.00 a gallon and premium is $2.20, your looking at just over $2 extra dollars a week or $120 a year.

It seems to me that there are far easier ways to save that much money without the risk of damaging your car and causing problems with the warranty by not following the manufacturer's specs.
posted by aaronh at 11:41 AM on May 21, 2005

Each of knave's comments are correct. Some of the other answers in this thread scare me.
posted by Kwantsar at 4:34 PM on May 21, 2005

I switched from regular to high octane petrol in my Subaru (which has a european-style engine) - no more pinging, significantly better acceleration, significantly better mileage. It's worth giving it a go.
posted by Jimbob at 5:23 PM on May 21, 2005

back in the late 1990s, before gas was so expensive, I had a second generation RX-7. I ran several tanks of regular, and several tanks of premium through the car, carefully recording the quantity of gas I added to each tank, the mileage obtained on the next tank, and the cost of gas.

It turned out that the premium gas cost less per mile than the regular gas. This may no longer be true, due to the higher spread between regular and premium. If your car does allow regular gas it makes sense to perform a similar experiment and discover for yourself whether "regular" gas is a false economy or not.
posted by b1tr0t at 5:44 PM on May 21, 2005

knave is right. Use what the manufacturer recommends unless you know better than the engineers.
posted by 6550 at 6:26 PM on May 21, 2005

oh yeah, i should revise my earlier comment -- my friend uses high-octane in a car for which 87 is recommended -- if the manufacturer says to use high octane, use it.
posted by fishfucker at 8:36 PM on May 21, 2005

Note that just because a car doesn't ping with lower than recommended octane doesn't mean it's running as good as it could. Lots of cars have knock sensors that will mess with timing if you use less than optimum gas. Those adjustments will negatively impact mileage and performance.
posted by Mitheral at 1:16 PM on May 25, 2005