Octane and MPG

Discussion in 'Fiesta ST Chat and Discussion' started by mcummings182, Oct 9, 2013.

  1. takuarc

    takuarc Member

    Lol can't agree more :) I live in South Africa.

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  3. Noah

    Noah Member

    Ah okay, it's probably Ron so in the USA Aki rating it's probably equivalent to 91 and 93. Not positive though. Highest I've ever seen not at a race track was 94 at a Sunoco near a racetrack, with the normal highest being 93
  4. integra

    integra New Member

    I always use RON 99 but I have tried RON 95 and I don't really notice any difference, I can get 44mpg but averaging around 35/37mpg. I've had the mountune upgrade giving me 215PS.
  5. TWDM

    TWDM Member

    Can you stop implying I am a cheapskate with your posts? I do not intend on using regular for your information. Please go check out the actual fuel economy estimates before you post random articles that don't mean anything. It clearly says regular gasoline. I don't need 10 articles to prove myself wrong. A simple Google search was extremely difficult.

  6. johnnyquest

    johnnyquest Member

    Well that's interesting. Clearly someone is lying or is grossly misinformed. But you know what, you sound like you're getting upset and tiring of this discussion. So, you win. I don't know what I'm talking about, and neither does Road and Track or Car and Driver. In fact, we should petition the oil companies to stop selling 89 and 91 octane fuel all together since there clearly isn't a need for it. And I will apologize for inferring that your position in the argument meant that you wanted to run 87 octane in your ST. You clearly never stated that in any of your posts, and I apologize for making that assumption.

    Enjoy your day.

  7. sumo64c

    sumo64c Member

    Hello all, just in from a 660 mile / 1452km interstate trip with the fiesta ST, at 75mph I averaged 34mpg, mileage now at 992 miles.
    Smokin likes this.
  8. johnnyquest

    johnnyquest Member

    Since I was bored I emailed the folks at fueleconomy.gov and received a very quick and informative response. TWDM, turns out Car and Driver left an important piece of information in their article. Because of our discussion, I've learned something new. Thanks.

    Dear Mr. Sandoval,

    Thank you for your interest in automotive fuel economy and your perceptive and well-researched question.

    The Car and Driver article is correct, but it would be misleading for us to state that the fuel economy values found on fueleconomy.gov are values that reflect the use of Premium fuel, because that’s not really the case. The fuel economy values measured in the laboratory do not go straight tofueleconomy.gov; rather, they are plugged into sets of equations that make adjustments for a number of factors on a nationwide average basis. We adjust the test values for a number of factors that can’t be replicated in the laboratory, including tire under-inflation, road grade (hills), road surface roughness, and, key to your question, fuel quality. Even though the tests may be run on Premium fuel, the results are adjusted to approximate a nationwide average fuel. Similarly, for a comparable example, the tests also assume level ground, but it would be incorrect to say that the EPA fuel economy values reflect driving on level ground because of the adjustments that are made to the test results.

    As far as what octane to use, the bottom line is that people should follow the recommendations or requirements as stated in their owners manual.

    I hope this helps, but do reply if you have additional questions.


    Rob French

    Roberts W. French, Jr.

    Environmental Protection Specialist

    Compliance Division

    National Vehicle and Fuel Emissions Laboratory

    2000 Traverwood Drive

    Ann Arbor, Michigan 48105

    Phone: (734) 214-4380

    Fax: (734) 214-4053

    From: John Sandoval [mailto:john.sandoval71@gmail.com]
    Sent: Monday, November 04, 2013 12:11 AM
    To: FuelEconomy
    Subject: [Fueleconomy] Request for clarification


    I was having a discussion with an acquaintance about fuel economy. He stated that the best fuel economy was to be had using 87 octane fuel, even if the vehicle is tuned for 91 octane fuel or higher. The vehicle we were discussing was the 2014 Ford Fiesta ST. According to your website, the MPG section has the words “Regular Fuel” listed.


    However, it is my understanding that the EPA uses either 93 octane or 91 octane “California Blend” that is specifically made for EPA testing to ensure repeatable results. I read this in the following article in Car and Driver:


    Could you please clarify this for me? And if it’s true you test your vehicles with 91 octane fuel or higher, could you please list that with your test results? By mis-stating the type of fuel used, it is possible that people with vehicles tuned for higher-octane fuel could be convinced to use 87 octane which, in most cases, will result in reduced power and engine efficiency, which could result in lower fuel economy.


    John Sandoval

    Tucson, AZ
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  9. Smokin

    Smokin Active Member

    Don't know what you're getting at but these cars will get better gas mileage with the recommended fuel, i.e.93 oct regardless if you're driving it like a granny or not. And the point is that it makes $2 difference per tank is a point well made.....

    Last winter in my GTI I decided to go cheap and put a couple of tanks of 87 oct in it and the mileage dropped significantly. From 27 to 23 mpg. And that was with 22 mile RT "granny" driving to work and back w/ overall avg speed per tank about 30 mph.
  10. TWDM

    TWDM Member

    My point is if premium really got better mileage then Ford would advertise their premium fuel economy, not the regular fuel economy. Rather than using non-standardized test results on completely different cars which really don't mean anything, I am sticking with the official numbers until shown otherwise.
    Last edited: Nov 5, 2013
  11. Noah

    Noah Member

    Winter Blend could of also accounted for the drop.

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  12. reddog99

    reddog99 Active Member

    Just to add another data point to the discussion and to further confuse everyone, here are the results of my own regular vs premium tests:
    The average of all my previous premium gas fill-ups (six tanks worth) is 32.8 mpg.
    The average of my last two regular gas fill-ups is 34.7 mpg.
    The figures are calculated manually at fill-up, not taken from the in-dash display. These results seems to be the opposite of what most people here are expecting and just goes to show how true the saying is, "Your mileage may vary".

    My commute is about 92 miles round trip from up in the mountains east of San Diego to the coast and back. The elevation changes from over 4000' to sea level and back, so I've got a pretty light throttle going downhill to work, and am running on the boost nearly all the way back home going uphill, so I'm assuming that it all evens out. The route is 98% freeway and my speeds mostly vary 65-75 depending on the traffic and daily jam-ups.

    It's obvious that if you want best performance, you should run premium. But for commuting, there appears to be no disadvantage to running regular.
  13. eRic

    eRic Active Member

    I'm almost at 2000 miles on my Fiesta ST and getting 27 mpg since the last fill up of 93 octane.
  14. audiphile

    audiphile Member

    These are my results. In the notes, I comment which octane I've been using. I alternate, and honestly it's a mixed bag. I've gotten exact same results with 87 and 93 with same type of driving. Note, that the comment of which grade I used applies to the NEXT mpg result.. ie, if I fill up with regular, the results show up at the next refueling.
  15. CarefreeAZ

    CarefreeAZ Active Member

    Here' s what I got. I'm trying different high octanes but haven't noticed any significant difference in performance/economy.

    Fuelly carefreeaz

    • 2014 Ford Fiesta ST
    • Gas Hatchback (Manual)
    • Sep-Nov 2013 • 33 fuel-ups (93/91 octane, Mobil/BP/Shell) • 6400 miles • 61% City/39% Highway 31.2 Avg MPG 37.7 Best MPG
    • 2011 Ford Fiesta SES
    • Gas L4 Hatchback (Auto)
    • Oct 2010-Nov 2013 • 168 fuel-ups (87/89 octane, Mobil) 58200 miles • 56% City/44% Highway 36.1 Avg MPG • 52.2 Best MPG
    Smokin likes this.
  16. rweidman

    rweidman New Member

    I would agree with carefreeAZ's numbers having a 2011 SES with manual. I did get a slightly higher mpg with the SES and did always notice a 2-3mpg increase with 0% ethanol gas. The ST can do 31mpg+with 0% ethanol but does drop down into the 27-29 range if I push the turbo.
  17. AlanBDahl

    AlanBDahl Active Member

    Holly Molly CarefreeAz, are you measuring in Imperial gallons or what? My best mpg in the ST is around your average and my worst (the last tank) is 25.7. Even in my old 2011 SES manual I think I only topped 37 mpg once and the average was in the 34-35 range. Are there no hills where you live? Or maybe you've learned some hyper mileing techniques you can share? Congratulations but I don't know what I can do to even get in your ballpark.
  18. WScottCross

    WScottCross Well-Known Member

    I'm averaging 30 so far, so 31 isn't unreasonable. I think the trick is in how light your right foot is. Very hard to get good milage in a car this fun!
    Firesail likes this.
  19. AlanBDahl

    AlanBDahl Active Member

    Commuting around here is a pain too. I think my average mph on the 25 mpg tank was about 25 too. Way too many cars and way too few roads and it's only going to get worse because they aren't building new ones while people are moving in in droves.
  20. WScottCross

    WScottCross Well-Known Member

    Traffic is relatively light here, so I'm sure that helps. Unless you have a hybrid, not much you can do to improve MPG in traffic.
  21. CarefreeAZ

    CarefreeAZ Active Member

    Well, with regard to the SES, the only times my mileage sucks are heavy A/C usage, hills/mountains (AZ), or winter stop-n-go (Midwest). With the auto, I think I've lucked out to get that good an MPG as I don't have many frequent highway drives. The ST is a different ball game as it's easy to get on it although I try to use the juice judiciously--100% city is probably 27-30, highway 65 mph is worth 35-38, but highway 75-80 mph is 30-32 at best. I'll have 7000 miles on the ST in a little over 2 months tomorrow so I've got a good handle on the mileage now. I've tried Mobil, BP/Amoco and Shell--93 octane/ethanol or 91 octane/no ethanol--but haven't noticed any difference in MPGs (hard to replicate drives for sure). The Mountune air box mod doesn't seem to have made any noticeable differences either.

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