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Cadillac STS Forum - 2005 through 2012 Discussion, Gas Mileage in Past Cadillac Vehicle Discussion; Start with a full tank. As Echas says, don't top it off and use the same pump. Note the miles ...
  1. #46
    malatu's Avatar
    malatu is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    Start with a full tank. As Echas says, don't top it off and use the same pump. Note the miles on odometer. Drive until tank is almost emtpy (if you are going to calculate the mpg for that one tank). Fill the tank up at same pump. Divide the miles driven by the gallons pumped into tank. If doing it with multiple tanks of gas use the same concept. Keep the receipts so you know how much total fuel pumped.

  2. #47
    dkozloski's Avatar
    dkozloski is online now Cadillac Owners 10000+ Posts
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    Re: Gas Mileage

    Quote Originally Posted by EChas3 View Post


    ----------

    Koz - Does the accuracy of your DIC vary in Winter?
    Not that I can tell.
    Don't mess with Binky Bear!


  3. #48
    cadillacmike68's Avatar
    cadillacmike68 is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    STS with a gas guzzler tax?? What years?? My 2009 doesn't 'qualify'

    I get:
    21-23 MPG at 75-77 MPH
    23-25 MPG at 70-71 MPH

    My 2000 ElDorado (ESC w 275 HP and less aggressive final drive ratio) got:
    24-25 at 74-75
    28-30 at 68-70

    All verified with the trip computer and fill-ups over time.

    My wife gets barely the same with her 2008 CTS (AWD)

    The Fleetwood can get over 21 MPG at 75 MPH or so, but only as long as its on the highway. Get off the highway, and it drops like a rock to 14-16 MPG

  4. #49
    jmildoc's Avatar
    jmildoc is offline Cadillac Owners Fanatic
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    I have been getting 23 mpg.

  5. #50
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    chazglenn3 is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    Quote Originally Posted by jmildoc View Post
    I have been getting 23 mpg.
    Is your profile out of date? It says you have a 01 Deville...23 mpg sounds right for a FWD NorthStar.

  6. #51
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Gas Mileage

    My AWD has the RPO R8E - GAS GUZZLER TAX. In mixed driving, I average about 17 MPG. Whenever I exceed 2,000 RPM consistently (accelerating or about 60 MPH on the highway) my mileage suffers, a lot! The Transmission Control Module programming also keeps it engaged in lower gears more than most American cars. It doesn't 'coast' much at all.

    My wife's 2007 RWD V8 can get 25MPG at 80 MPH of pure Interstate cruising (2,000 RPM). It coasts almost as well as my old Buick Roadmaster. Nothing coasts like a 3800 Park Avenue!

  7. #52
    cadillacmike68's Avatar
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    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    how do U do Ur manual calcs?
    In longhand.

    1. Fill the tank and let the auto shutoff stop
    2. set your trip odometers to zero, set the avg MPG to zero as well
    3. drive for 1-3 days, note the total miles driven
    4. go back to that SAME pump and re-fill the tank the same way
    5. note the gallons used.
    6. divide the gallons used into the miles driven. Compare with the avg MPG. They should be no more than 10% different from each other. Say hand calc is 15.4 and DIC says 14.6 that's about 0.8 out of 15.4 or about 5.1% difference which is ok by me. If the DIC is more than 10% lower than the hand calc, something is off.

    And yes AWD really SUCKS GAS in these cars. My wife;s 2008 CTS V6 DI AWD is worse than my 2009 N* STS

  8. #53
    DdoubleE is offline Cadillac Owners Member
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    Does it really make a difference on what type of fuel you use? I have a 06 STS and I use 93, but would I lose any gas mileage or power if I switched to 91 mid grade?

  9. #54
    jmildoc's Avatar
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    Quote Originally Posted by chazglenn3 View Post
    Is your profile out of date? It says you have a 01 Deville...23 mpg sounds right for a FWD NorthStar.
    I hope my mpg stays the same with my new wheels. I got the 17's on now

  10. #55
    EChas3's Avatar
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    Re: Gas Mileage

    YMMV!

    Yes, the type of fuel can matter in several ways. Cadillac recommends higher grades but they aren't required by the Northstar V8. My mileage and performance seems the same on all grades, so I use 87. In my area, all gas is the same RFG 10% Ethanol. Whenever I can get 100% gas, I do so. Ethanol is a poor fuel; costly and bad for the environment.

    If your car runs better on 91 Octane, you should use it.

    Your most important choice is to use a Top Tier gas that contains the fuel additives recommended. Go to http://www.toptiergas.com/.

  11. #56
    MacMuse's Avatar
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    I definitely notice a difference in engine responsiveness at normal driving speeds when I drop to 89 Octane. I'm sure the difference is less pronounced at mid-grade. Run your tank down to under 40 miles left on the DIC, and then try out a tank for yourself. It comes down to how you drive and whether you'll notice and/or tolerate the responsiveness drop-off.

    2nd the TopTier recommendation. I only use TopTier despite the 3-5 cent per gallon bump from the brand name shops. After all, advertising on network TV isn't free! I'm approaching 100K miles on my '06 (65K in my 3 years in the car), and I've never had a single fuel related incident or even a ping.

  12. #57
    DdoubleE is offline Cadillac Owners Member
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    For the year I've had the car I've always used 93. I was just curious if the other grades made a difference. I like the get up and go I get, so I will stick with 93.

  13. #58
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    My 2000 DTS averages between 16-18mpg with 50/50 city/highway. Oh and that's with a cylinder misfiring. My new 2005 STS with the V8 is averaging 19-22mpg under the the same conditions. I believe anywhere near 20mpg consistently is fine! This is my 3rd Cadillac and I'm already looking forward to my 4th lol!!

  14. #59
    sztolcaddy is offline Cadillac Owners Member
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    Re: Gas Mileage

    Mileage of my 2005 STS v8 sucked and I had several issues with battery not starting (thank car gods for major GM guard), after replacement of the battery by the dealer the gas mileage improved significantly, I guess alternator was constantly charging the dying battery. Now even the memory seat works, I guess car was shutting down accessories to save the battery. Unfortunately battery wasn't covered by extended warranty. Now in the mostly street driving I get 19 mpg if i drive on freeways, but within a smaller streets and hills it drops to 15.1, was having 12-13 before.

  15. #60
    jmildoc's Avatar
    jmildoc is offline Cadillac Owners Fanatic
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    I switched to 89 octane and my MPG went down 1.6 mpg?!?!?!

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