Using Lower Octane in the Winter

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221
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IL
Had a question about this topic. My Mini Cooper requires 91+/premium fuel, which in my area equates to 93 octane. I'm not asking this out of cheapness or frugality, but I'm genuinely wondering: would 89 octane actually be BETTER to run in the winter than 93? To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes. The air is denser, which makes the air/fuel leaner. The air is colder, which resists knock better. Which of these factors "wins" out? Are there other factors aside from detergents in 93? I liken driving in the winter to running a cold air intake, in any case anything you use to cool the air/fuel lets u run leaner and produce more power - on the flip side, can you run a lower octane?
 
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CT8

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Carb crush or fuel injection? Not many carbed cars around. So I would imagine within the parameters of the electronics ability to adjust the air fuel rations as programmed I don't know.
 
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Originally Posted By: kyoo
Had a question about this topic. My Mini Cooper requires 91+/premium fuel, which in my area equates to 93 octane. I'm not asking this out of cheapness or frugality, but I'm genuinely wondering: would 89 octane actually be BETTER to run in the winter than 93? To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes. The air is denser, which makes the air/fuel leaner. The air is colder, which resists knock better. Which of these factors "wins" out? Are there other factors aside from detergents in 93? I liken driving in the winter to running a cold air intake, in any case anything you use to cool the air/fuel lets u run leaner and produce more power - on the flip side, can you run a lower octane?
The mixture is not leaner.....The ECU compensates for thicker air, and adds fuel. Anyway, you could run on 87 all the time, but you would lose some performance in circumstance other than what you are outlining. In other words, no harm will occur regardless, and you are probably correct in your assumption that, with an engine that is never getting to design temperature, you can run lower octane, and possibly even get slightly better performance.
 
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Originally Posted By: kyoo
The air is denser, which makes the air/fuel leaner.
No. Reachier. More oxygen in the same amount of air. To preserve same air/fuel ratio, more fuel is required. That's how cold air intake works.
Originally Posted By: kyoo
The air is colder, which resists knock better.
These two facts are not related, IMO.
Originally Posted By: kyoo
can you run a lower octane?
No. The only place where you can use lower octane fuel is mountains.
 
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beaver land EH?
@CT8: If you read carefully, OP is referring to his/her 2013 mini, which is OBD-II based EFI engine. If your engine has knock-sensor and engine ignition mapping can accommodate lower octane rating (say, 87) with reduction in power output, then yeah, can't see any reason why(not) to run 87 octane gas. Q.
 
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Why not try it? If you burn top tier gasoline would not worry about detergents. At one time here in the Southeast Shell said that their 93 Octane contained more detergents that lower octane gasoline they sold but all of their gasoline is rated as top tier and at least here 89 octane is a mixture of 87 and 93 octane as there are two tanks underground hence the mixture by the pump. Haven't seen that sign about the 93 octane at the pumps for awhile here.
 
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I'm not sure where better performance would come from. Your engine will have intake air temperature in open loop and compensate for it. In closed loop the AFR will be the same regardless of temp. Your engine doesn't run richer or leaner based on temp. Sure, perhaps in your application you could run regular and never get knock due to low temps and light loads.
 
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Try it, its not a high specific output turbo. I cant see a cold head pre-igniting. I agree with Q., and that most engine employ a Knock sensor. Now 2 the miles commute is and issue for your car. Can you bike? Yours is really a situation for a hybrid that will run on BAtt for 15 miles up to 30 mph.
 

CT8

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Originally Posted By: Quest
@CT8: If you read carefully, OP is referring to his/her 2013 mini, which is OBD-II based EFI engine. If your engine has knock-sensor and engine ignition mapping can accommodate lower octane rating (say, 87) with reduction in power output, then yeah, can't see any reason why(not) to run 87 octane gas. Q.
Did you read my whole post.
 

kyoo

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OP here - you CAN run 87, 89 per the owner's manual - they just outline an increased chance of knock. I guess the question is, are you less likely to knock in cold air than hot air? If so, enough to run a lower octane?
 

CT8

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Originally Posted By: timeau
Originally Posted By: kyoo
The air is denser, which makes the air/fuel leaner.
No. Reachier. More oxygen in the same amount of air. To preserve same air/fuel ratio, more fuel is required. That's how cold air intake works.
Originally Posted By: kyoo
The air is colder, which resists knock better.
These two facts are not related, IMO.
Originally Posted By: kyoo
can you run a lower octane?
No. The only place where you can use lower octane fuel is mountains.
the electronic these days are functionally so similar as far as their inputs and outputs that they can functionally considered almost all the same.
 

kyoo

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Originally Posted By: ARCOgraphite
Try it, its not a high specific output turbo. I cant see a cold head pre-igniting. I agree with Q., and that most engine employ a Knock sensor. Now 2 the miles commute is and issue for your car. Can you bike? Yours is really a situation for a hybrid that will run on BAtt for 15 miles up to 30 mph.
Pretty cold to bike, I did in the summer for a little before the bike was stolen. Battery/Hybrid would be nice, but I wouldn't change cars just for this situation. Just wondering if 89 will burn better/more appropriately
 
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Given the age and warranty of the car, I would say run what it requires as it is tuned for that fuel grade. If you had to do a longer run somewhere there could be issues until it is out of the system. It never fully warms up, probably never gets out of cold engine/open loop fuel map. I would be more worried about making sure the oil is in good shape than the fuel. After the warranty do what you want, but I would also consult your Mini forums as this is a pretty model specific question at that point.
 

sds

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18
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MA
Originally Posted By: kyoo
Had a question about this topic. My Mini Cooper requires 91+/premium fuel, which in my area equates to 93 octane. I'm not asking this out of cheapness or frugality, but I'm genuinely wondering: would 89 octane actually be BETTER to run in the winter than 93? To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes. The air is denser, which makes the air/fuel leaner. The air is colder, which resists knock better. Which of these factors "wins" out? Are there other factors aside from detergents in 93? I liken driving in the winter to running a cold air intake, in any case anything you use to cool the air/fuel lets u run leaner and produce more power - on the flip side, can you run a lower octane?
You're thinking too much--the temperature of the igniting fuel in the motor is not very dependent on ambient air temperatures. There's simply not enough thermal mass in the air entering the motor to alter the temperature of the flame. I would run 93--while the motor can compensate for knock, it needs to knock before it compensates. I personally would rather not have the motor knock in the first place. Also, the engineers at Mini have most certainly accounted for ambient temperature variations and cold starts when recommending fuel grade. Again, you're overthinking here.
 
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I believe on the west coast they use more premium so it's typically 91 octane for super over there while on the east coast there's more 93 octane. So the auto manufacturers design for 91 octane because they don't know which coast the car is going to end up at. You can get to 91 octane just by mixing 1/3 87 regular and 2/3 93 octane. The gas stations just mix 87 and 93 to get to 89. It's just 1/3 super to 2/3 regular. If you do the math, the gas stations typically charge a little bit more for plus than if you just did the mix yourself with regular and super.
 
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ME
I did it with a volvo turbo wagon in the dead of winter. I'd get 87 if the spread to high octane was more than 30-40 cents. I aimed to get every other fill high-test, and every other, other fill regular. I filled at 1/2 tank. The car ran different; it used a simple TV cable for shift points and I noticed I was into the gas more for a given amount of power, which delayed shifts slightly. I never drove like a bozo as I was on studded snow tires and sometimes on an icy surface. My way of thinking was the 87 was fresher and more likely to "light off" well with a cold start. Whatever, it worked.
 

kyoo

Thread starter
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IL
well i'd run 89 if anything. i think this is kind of one of those things like - is it recommended to do? not really. is it gonna cause any harm? most likely not. i may give it a shot, why not. i have a hard time believing that, in my particular conditions, the engine would knock anyway, even on 87, let alone 89
 
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Boston, MA
Originally Posted By: kyoo
Had a question about this topic. My Mini Cooper requires 91+/premium fuel, which in my area equates to 93 octane. I'm not asking this out of cheapness or frugality, but I'm genuinely wondering: would 89 octane actually be BETTER to run in the winter than 93? To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes. The air is denser, which makes the air/fuel leaner. The air is colder, which resists knock better. Which of these factors "wins" out? Are there other factors aside from detergents in 93? I liken driving in the winter to running a cold air intake, in any case anything you use to cool the air/fuel lets u run leaner and produce more power - on the flip side, can you run a lower octane?
Richer mixtures knock less. Before FI systems and their built in compensation for air mass and temp this might have been an issue.
 
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The time to "drop an octane level" is long interstate drives. Low throttle, high manifold vacuum, steady throttle driving greatly reduces the octane requirement of an engine. Crossing Texas on Interstate 10 is no place to waste 93 Octane gas!
 
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