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Difference in gasoline quality

  1. Aug 20, 2009 #1
    Is there a difference in the quality of gasoline among different companies? I see Shell gas station sells premium unleaded (9/10) for 3:00/gallon, and across the street, Rotten Robie sells the same premium unleaded (9/10) for 2:60. I assume shell station might provide a better service (accepting almost all credit card, whereas in the Rotten Robie, you might have to pay by cash). But, for the automobile, is there a difference?

    Another one, Chevron advertise on a fuel additive called Techron. Do you see any difference in fuel efficiency if you use Chevron gasoline?
     
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  3. Aug 20, 2009 #2

    mgb_phys

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    In most places there are only a few producers of gasoline, so even big names might be getting it from the same refinery. Supermarkets will buy from whoever is giving the best price, independants are usually stuck with whoever will deal with such a small customer.
    Generally the fuel sales just cover the rent - the profit is made on selling food/drinks. This is even true of big name gas stations - most of them are franchises.

    The fuel grade is closely monitored by trading standards (or equivalent) and additives that claim to boost power/performance/mileage are generally lying.
    The detergents (Techron) are genuine, they claim to reduce emissions, although how necessary they are is a bit debatable .
     
    Last edited: Aug 20, 2009
  4. Aug 20, 2009 #3

    turbo

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    Yep! Depending on where you live, all the gasoline in your region could come from one tank-farm. Apart from octane rating and % ethanol (if any) the only difference in the fuels is in the additive packs that the tank-truck drivers dump into the tanks before filling them at the tank farm. I tend to buy Irving gas (NB company) because they satisfied BMW's cleanliness standard for fuel-injectors. They have their own refinery, and a large chain of convenience stores all across Maine and into NH.
     
  5. Aug 20, 2009 #4
    So the conclusion is all the gasoline are the same, it's the detergent that's different among brands. Some google search pointed me to a site http://www.toptiergas.com/index.html.
    As per them, the TOP TIER Detergent Gasoline Retailers are (I think it's not in any particular order)

    QuikTrip
    Chevron
    Texaco
    MFA Oil Co.
    Conoco
    Phillips 66
    76
    Entec Stations
    Shell
    The Somerset Refinery, Inc.
    Kwik Trip / Kwik Star
    Aloha Petroleum
    Tri-Par Oil Co.
    Turkey Hill Minit Markets
    Mileage Stations
    Chevron Canada
    Shell Canada
    Petro-Canada
    Sunoco Canada
     
  6. Aug 20, 2009 #5

    Astronuc

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    The quality of the gasoline depends on the refinery.

    I've used Mobil gasoline, but since Exxon merged with Mobil, I don't know if that's what I'm getting. Our area has mandatory ethanol additives, and I'm not sure how good that is.

    I have also used Shell in the past, and that was OK.

    I used to get Texaco once in a while, but the engine performance seem to decrease. That might have been due to lesser quality gasoline at the particular stations.
     
  7. Aug 20, 2009 #6

    brewnog

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    The quality does vary slightly between refinieries, but in the past 5-10 years or so, it's all so well controlled the differences are tiny and don't make any practical difference as far as performance or durability are concerned.

    Buy on price or convenience.
     
  8. Aug 20, 2009 #7

    russ_watters

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    ...And don't buy "premium" (which is just a useless marketing word) unless your engine requires the higher octane rating. Higher octane is not better it is just different.
     
  9. Aug 20, 2009 #8
    it's less that different. has less heat energy. but either way, it's a waste in engines that don't require it. the higher octane is just so that you don't get early detonation in high-compression engines (turbos, superchargers, high stroke compression).


    about the detergents thing, i suspect it is mainly to keep the fuel injectors clean so that you don't get decreased air/fuel mixture efficiency or uneven dispersal between cylinders. keeping the throttle body clean is also important.
     
  10. Aug 20, 2009 #9
    But none of the brands talk about the performance improvement (on using detergent) quantitatively. They all use just marketing words like "cleaner", "more efficient" etc. I'm wondering if the performance improvement we get is not worth the premium we pay.
     
  11. Aug 20, 2009 #10

    turbo

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    I always buy the lowest-octane grade from a brand/station that I trust. The only time that I had to buy higher-grade gas was when I owned a HD Wide Glide that had extensive head-work, steep cams and other modifications. I could get by with mid-grade gas in cool weather, but when the weather got warm or hot, high-octane fuel was essential to prevent pinging and knocking. Pre-ignition does not just rob performance, it can damage a high-performance engine.
     
  12. Aug 20, 2009 #11
    not sure how big of a problem it is, but i've always heard to buy your gas from a station doing good volume of business, to avoid getting water in the gas. i really have no qualms about buying gas from a non-brand-name, if their throughput is high.
     
  13. Aug 20, 2009 #12

    dlgoff

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    Here in Kansas I buy 10% ethanol with a 89 octane for 10 cents a gallon less than the regular 87 octane. Put over 200K miles on the old buick and have never had to replace any injectors. And she still gets 30+mpg on the road with her 3.3 liter.
     
  14. Aug 20, 2009 #13

    russ_watters

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    I always thought that the differences were negligible, but I'm seeing some links that say higher octane gases have more energy, not less. Do you have any sources you can post that attest to your belief? Here's one I found:
    http://www.api.org/aboutoilgas/gasoline/gasoline-octane.cfm
     
  15. Aug 20, 2009 #14
    Different oil companies will pull up tankers to the same refinery and same spigot, though the blends they contract are different.
     
  16. Aug 20, 2009 #15
    i assume you are also seeing links that say the reverse? my memory is obviously not perfect, but that is what i was going by. the wiki page is a bit incomplete, but for at least alcohol blends, the energy content is lower.

    http://en.wikipedia.org/wiki/Gasoline#Energy_content
     
  17. Aug 20, 2009 #16

    russ_watters

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    I googled "gasoline octane vs energy content".
    I did see that, I'm just not certain it applies to gasoline.
     
  18. Aug 20, 2009 #17
    it may very well be a neglible difference, though i'm not quite sure what to make of a reference from the PR agency for the industry.

    i will look a little more, but it doesn't seem easy info to conjure.
     
  19. Aug 20, 2009 #18

    S_Happens

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    It's not a case of one or the other. The octane rating and heat energy are independant of one another. It would entirely depend on the blend, as gasoline is a term used to describe a wide variety of fuel mixtures.
     
  20. Aug 20, 2009 #19
    Well, higher "octane" refers to a fraction that contains, on average, longer chain molecules that are less susceptible to pre-ignition, as already noted. The lighter fractions have fewer carbon-carbon bonds to break measured by mass, and should have higher energy content, would be my guess. However, the lighter fractions are less dense in the liquid state, aren't they? The idea is to measure by the gallon. Where's a chemist when you need 'em?

    Edit: We might get an idea in the Wikipedia article, examining the trend from lighter to heavier fuels from 87 octane gasoline, to jet fuel, to diesel.

    87 octane --- 125,000 BTU per US gallon
    ...Jet Fuel --- 125,930
    ......Diesel --- 138,700

    I think this would place 90 octane gasoline at only couple percent lower in energy content than 87 octane.
     
    Last edited: Aug 20, 2009
  21. Aug 20, 2009 #20

    S_Happens

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    Not to be too nitpicky, but pre-ignition is not the same as detonation. In this discussion about octane, it is detonation that we are referring to.

    The wikipedia reference you use is far too general to be of any use. There are different blends of gasoline, even within the same octane rating, to apply a specific amount of energy like that. The (R+M)/2 rating that you see at gas pumps is simply a rating based on resistance to detonation under certain conditions.

    I guess you can come up with a rule of thumb if you want, but it will be too general to be of any practical use.
     
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