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What about fuel types & gas mileage?



  • shiposhipo Posts: 9,152
    While it is unlikely that your engine will ping, it fairly certain that both performance and fuel economy will suffer. Long story short, it will cost you less to use premium fuel in the car.
  • mbowen1989mbowen1989 Posts: 8
    Ok, what premium gas is is 93(Most cars in this case recommend 91 because of Cali.). Which is a octane number for that grade of gas. So in a nutshell the higher compression of the engine the more likely the fuel is to pre-ignite (burns w/o use of spark plug). Thus we run higher octane, meaning that higher octane resists pre-ignition. So running 87 will case a lack of performance due to the knock sensor. And what that does is senses the pre-igntion happening and retards the timing(Opposite of advancing) Thus causing you to lose horsepower. As far as gas mileage goes, you'll lose some MPG's as well. Hope I was not to confusing. Fell free to ask any questions or if you need me to explain more on something else.
  • shiposhipo Posts: 9,152
    "Ok, what premium gas is is 93(Most cars in this case recommend 91 because of Cali.). Which is a octane number for that grade of gas."

    The AKI (Anti Knock Index) of fuels sold in the States and Canada (and Mexico too?) is an average of two different Octane ratings (i.e. (RON + MON) / 2), and as such it isn't actually an octane rating in and of itself.

    "So in a nutshell the higher compression of the engine the more likely the fuel is to pre-ignite (burns w/o use of spark plug)."

    Ummm, no. The AKI rating of a fuel has virtually nothing to do with pre-ignition as there isn't a single car sold anywhere in North America that will experience pre-ignition on any grade of gasoline sold here. Where the AKI does come into play is in preventing detonation or "knocking" (hence the name) under normal operation.

    A few definitions to help you out:

    - Detonation: Detonation occurrs when small pockets of end gas (i.e. unburnt pockets of air and fuel) exceed some critical temperature and/or pressure (varies by combustion chamber design, combustion chamber condition, air/fuel mixture and fuel grade) and spontaniously combusts before the flame front reaches said pockets. A key point here is that detonation happens long after (relatively speaking) the spark event.

    - Pre-ignition: The spontanious combustion of fuel before the spark event. Pre-ignition will never-EVER occur, regardless of the grade of fuel, unless the engine has a serious problem, and should such a problem exist, no grade of fuel will prevent it from happening and almost instantly destroying the engine.
  • steverstever Posts: 52,683
    A journalist would like to speak to someone who fuels up with 85 octane and has experienced engine issues or a weaker performance at lower elevations because of it. If you use or have used 85 octane, and would like to share your story with a reporter, please send your daytime contact info to no later than Wednesday, June 20 at 2 p.m. Pacific/5 p.m. Eastern.
  • 43mary43mary Posts: 3
    I have had a stalling and hesitation problems with my 2012 X3 when temperatures dip below - 3 C for nearly a year now. BMW maintains that this is a wide spread problem with this engine and is caused by premium fuel. In their words, BMW designed the award winning engine for a specific type of fuel and without telling BMW the fuel manufacturers changed their formulations and now the engine stalls in cold weather. I live in the Northeast, by the way. Their suggested fix , which did not come by way of a service bulletin by from an email to the service dept from a regional technician based on what he has done with his own vehicle, is to use regular gasoline until it warms up as it is only a problem with winter formulations. They can't explain why not all cars are affected. I have contacted gas manufacturers and have heard from one so far. They would like BMW to explain themselves as their fuel meets TOP TIER requirements. I can't imagine what mileage I can expect nor the possible engine damage over time. Anyone else with this problem?
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 57,595
    It seems unlikely to me, although I'm not a trained petroleum engineer, that a fuel would stall a car when cold but leave it to run perfectly when warm. I'd like to know how BMW explains that scientifically, and by what testing they came to the conclusion. My mind's open to it but I suspect that the car's computer, or "map", isn't dialed in quite right and might need a software upgrade fact, this is a widespread problem and not isolated to a few cars.

    Other ideas come to mind---such as a faulty coolant temperature sensor.

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  • eliaselias Posts: 2,120
    it makes sense to use regular gasoline in winter in any car that can accept it, including those for which premium is 'recommended'. (i've done so for decades in 5 or 10 cars, including as recently as this week...)

    no matter the formulation, 87 ignites more easily than premium, by definition.

    so if BMW recommends 87 as the solution, and it works for you, then i don't see any issue. happy motoring!
  • 43mary43mary Posts: 3
    Thanks for providing your experience with 87.

    It's one thing to use this gas by choice quite another when it is required to get your new engine to start when temperatures dip slightly below freezing. I did not expect a seasonal vehicle.

    BMW is not referring to octane but so called changes to the premium fuel additives by manufacturers "after they designed the engine" forcing BMW to "rush to catch up" according to my dealership. No specific manufacturer is mentioned so I'm currently contacting all. So far the response has been that BMW's claim is senseless and BMW has never contacted them. They ask that BMW to do so as gasoline is highly regulated.

    If BMW recommends this fuel, let them formalize it in a service bulletin and change their literature re their recommendation of premium fuel for mileage, performance and engine maintenance.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 57,595
    edited January 2013
    Well no arguing if something actually solves the problem, but I'll believe it when I see it---that fuel alone can cure a stubborn stalling problem so reliably that every other cause could be eliminated. ( see below for what I mean)

    As for 'burning faster', I don't think this is inherent in the 87 fuel---what I think might happen is that the regular fuel will signal the car's computer to retard the ignition timing (giving you less power and performance by the way), and thus, ignition might occur a bit sooner---so in THAT sense it burns, not faster, but sooner, in the combustion chamber.

    On the other hand, any fuel with ethanol would burn FASTER.

    My two cents.

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  • eliaselias Posts: 2,120
    edited January 2013
    octane is by-definition a measure of: resistance to detonation. a measure of the resistance to the initial ignition. far as i understand it...

    also iirc, independent of top-tier or bottom-tier gas, it's been decades since there were different additives in different grades of fuel - except for variations required to change octane & maintain the govt-mandated oxygenation.

    Clearly BMW has a 'bug' to fix with the vehicle and a TSB may be appropriate if the issue is common.

    Owners who prefer to spend more per gallon to get identical winter performance by running premium fuel should be forewarned that the x3 may not be the right vehicle for them.

    i wonder if the BMW does better with unoxygenated/minimally-oxygenated 91+ octane? (you may have to drive >500 or >1000 miles to find any, maybe not worth it just to find out :| ;).
  • srs_49srs_49 Posts: 1,394
    octane is by-definition a measure of: resistance to detonation. a measure of the resistance to the initial ignition. ...

    Your first statement is correct, but not the second. There is no difference that I know of in the ease with which 87 octane gas ignites in the presence of a spark verses 91 octane.

    So I don't understand why using 87 octane in the BMW would solve the problem she mentioned. Unless it's related to the winter time formulation of the gas where she lives - which is what I think you were getting at.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 57,595
    Exactly. My personal opinion is that the explanation given by BMW is, as we used to say, "the sunshine treatment". We park your car for a day, tell you it's all better, and hope you go away.

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  • eliaselias Posts: 2,120
    regular fuel fixed the problem with the BMW, if i read the initial post.
    so the techs did in fact fix the problem. if not then its gotta be fuelpump or injector issue?

    assuming i read correctly that the original problem was actually solved by using the supported 87 octane, it can addressed by adding 4 words to the owners manual:
    "premium fuel is recommended, EXCEPT IN FREEZING WEATHER".

    some time maybe you will encounter non-start situation in frigid weather with whatever engine and if you have lower-octane fuel available, maybe you'll see it work...

    (btw, so i see your point correctly that the octane measures the resistance to pressure-induced ignition, not sparked ignition?!)

    in any case, i'm wishing to go back to a diesel engine, so looking forward to our ongoing different stylings regarding CETANE . never mind all this octane stuff.

    one of the automags years ago (before oxygenated gas became required in USA) put a big v8 crate engine on a bench and tested it with the various octanes, as well as precisely measuring the tiny octane differences in the gasolihe. it was amazing how little difference the octane was, and how little difference in performance actually resulted.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 57,595
    edited January 2013
    yes but that's anecdotal, and anecdotes are not evidence. Stalling can be caused by so many factors that we have to be careful, if we wish to be good diagnosticians, --we have to be careful not to confuse causation with correlation.

    chances are pretty good that someone else with a similar problem will not find regular gas to be a solution.

    I suppose it would be fair, at least at this point, to say that using regular gas does not "cure" cold start stalling in an X3, but that it may, under certain circumstances, alleviate it in certain cars?

    The bench test with the big V-8 would be meaningless if the engine didn't have computer controls for timing I think, because all they had to do was set the timing to just short of the ping point on regular fuel---and then yeah, sure, using higher octane wouldn't matter much at all. There isn't any more "power" in high octane gas.

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  • eliaselias Posts: 2,120
    edited January 2013
    yeah... it was a racer-type magazine that tested those V8s, i'm sure they did not omit the knock sensors... pretty sure knock sensors are 'standard' on GM V8s for decades.

    anyway, "YMMV" ! :) speaking of BMWs and fuel types, I've been seeing so many X5d lately! must be nice to drive one of those ....
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 57,595
    I think knock sensors came out in 1981 or so.

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