Where are my MPG going?
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  • 1 Post By Submariner409
Cadillac DTS Forum - 2006 through 2012 Discussion, Where are my MPG going? in Past Cadillac Vehicle Discussion; My car was holding pretty steady at 17 MPG which seems kind of low from what everyone else on here ...
  1. #1
    TLC
    TLC is offline Cadillac Owners Member
    Automobile(s): 2006 DTS
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    Where are my MPG going?

    My car was holding pretty steady at 17 MPG which seems kind of low from what everyone else on here is reporting there's to be but I attributed that to my being a lead foot and loving how my car feels under power. lol But lately it's dropped down to 15.6. My first thought was maybe because it's now winter but we havent really had much snow and I noticed this drop before it snowed at all. Could there be an issue here like plug, wires, or something. And more importantly could it be nothing and I'm just paying to much attention to my car? lol

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  3. #2
    Superjim's Avatar
    Superjim is offline Cadillac Owners Connoisseur
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    Re: Where are my MPG going?

    Quote Originally Posted by TLC View Post
    My car was holding pretty steady at 17 MPG which seems kind of low from what everyone else on here is reporting there's to be but I attributed that to my being a lead foot and loving how my car feels under power. lol But lately it's dropped down to 15.6. My first thought was maybe because it's now winter but we havent really had much snow and I noticed this drop before it snowed at all. Could there be an issue here like plug, wires, or something. And more importantly could it be nothing and I'm just paying to much attention to my car? lol
    That is very possible... also with the cold weather, it will take longer to warm up and go into CLOSED LOOP mode.
    As long as it is in OPEN LOOP mode, the mixture runs a good bit richer... which would make it use more fuel... especially if a lot of your driving is less than 5 mile trips.

  4. #3
    TulsaVic is offline Cadillac Owners Enthusiast
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    Re: Where are my MPG going?

    I typically loose 2 mpg in winter during routine driving. Trip mpg, when the car has ample time to totally warm up, usually is the same summer/winter.

  5. #4
    tonyb71's Avatar
    tonyb71 is offline Cadillac Owners Member
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    We were discussing fuel octane on another thread, and the thought is that 93 will give you a few more mpg.

  6. #5
    Tom's Caddy's Avatar
    Tom's Caddy is offline Cadillac Owners Fanatic
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    Re: Where are my MPG going?

    My MPG goes down 1.5-2.5 in the winter always, but I let it warm up for 5 minutes which brings the MPG down. Like the steering wheel warm.

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Where are my MPG going?

    Just like your bones on a cold winter morning, it takes more power to move the car when everything is stiff - less fuel mileage. The differences in mileage between gasolines/octanes is small enough to be inconsequential. (Not one tank difference - 500 or more miles of records.

    "But, Sub, I put in half a tank of 93 and got great mileage !" Let's see - 18 gallon tank, 87 octane; half fill with 93 = 90 octane in the tank. How many refills do you need to get to pure "93" ?

    ........... and, as Tom's Caddy posted, at 0 mph your gas mileage is 0 mpg - and that long-term calculated average drops like a rock.
    Tom's Caddy likes this.

  8. #7
    jstynjudge's Avatar
    jstynjudge is offline Cadillac Owners Member
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    Re: Where are my MPG going?

    I have found that 91 octane in the winter months will do you better on gas mileage than 93. I live in southwestern Pa in the Laurel Highlands. With an average temp of 21-29 degrees fahrenheit running 91 octane I still lost 3-4 mpg in the winter months. I lost 6-7 mpg running 93 in the winter months. I don't even touch lower octanes ingrained in me from my 4.9 Fleetwood. On warmer days I get 22-24. During the winter I averaged about 18.8 mpg.

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