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Cadillac STS Forum - 2005 through 2012 Discussion, Gas Mileage in Past Cadillac Vehicle Discussion; Bravo! If I could only get this across to my wife who is still on the gas 50 yards from ...
  1. #76
    malatu's Avatar
    malatu is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    Bravo! If I could only get this across to my wife who is still on the gas 50 yards from a stop sign!

    Quote Originally Posted by mckellyb View Post
    I experimented with several tanks of 87 vs. 93. No difference in performance or MPG I could detect. I didn't expect to feel a difference in performance. Anything less than 10% on a car of this power, isn't going to be felt by anyone other than maybe a professional test driver.

    My MPG varies little, because my drive varies little. The car is used almost exclusively for commuting, and my commute could not be any less variable.

    Per calculations based on the trip odo and pump gallons...the DIC reads both high and has variance...I get 21.2-21.5. The difference could be oneparticularly bad day of traffic or I stomped on it a couple of times, letting that Northstar wail. Well, occasionally, I'll be lucky and catch a few lights in a row green.

    Tire width plays a part in MPG, as does, believe it or not, tread patterns. On these cars, you're never going to see a difference of 20mm in width. That's less than an inch per tire. Meh.

    Now, if you put 155/85/16's on it, you might see MPG go up one or two, but you'd hate yourself for trying it out.

    One thing people can do to increase MPG is to look ahead. Yes, I'm yelling.

    Watch for traffic changes, lights with an old green or turning yellow/already read, et cetera. Most people can increase their MPG a solid 20% just by backing off, and not always having one pedal in use. The car and associated wear items last longer, passengers have a smoother ride, and you spend less money.

  2. #77
    Midnight is offline Cadillac Owners Fanatic
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    Re: Gas Mileage

    Quote Originally Posted by malatu View Post
    Miles per tank really doesn't say anything, comparatively speaking.
    I wish it did! I get some truly inspiring miles per tank sometimes. I have literally rolled into a gas station once, just as I ran out of fuel and the engine stopped. Not this car though. But I am still an experienced hyper-tanker, a white-knuckled pusher of the limit of how far below the E you can actually go...

  3. #78
    mckellyb is offline Cadillac Owners Enthusiast
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    Re: Gas Mileage

    Quote Originally Posted by malatu View Post
    Bravo! If I could only get this across to my wife who is still on the gas 50 yards from a stop sign!
    Yeah, it's a tough concept to get across to many folks. Even more so if they've not driven a manual transmission on a regular basis. It helps to show them on a bicycle. Have them pedal right up to when they'll have to brake to a stop, and they'll understand.

    It kills me to see people rush right up to a light, which I backed off for 15 seconds earlier, only to have it change as I get to it, and I never had to touch the brakes. Bonus: I'm now ahead (though I could not care less).

    The two freeway exits I use daily are like this. I know them well enough to know exactly where I can start 'coasting', and not suffer less than 0.5 second of an inconvenience, if that. I have to stop and wait for traffic at the end of both 99% of the time, so the best solution is not to hurry up and wait.

  4. #79
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    maiahsdad is offline Cadillac Owners Fanatic
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    I filled my tank with 93 OCTANE at the BP station before leaving Indianapolis going to Ohio. 305 miles out of that tank.

    Filled up with 87% octane at a BP station in Ohio before leaving for Indianapolis. 318 miles out of that.one.

  5. #80
    malatu's Avatar
    malatu is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    I filled my tank with 93 OCTANE at the BP station before leaving Indianapolis going to Ohio. 305 miles out of that tank.

    Filled up with 87% octane at a BP station in Ohio before leaving for Indianapolis. 318 miles out of that.one.
    That means absolutely nothing unless you know exactly how may gallons it took to travel the mileage you recorded. Remember, the benchmark that is use to determine the efficiency, is miles per gallon, not miles per tank!

    So there was a difference of 13 miles beween the two trips. You know how many miles each trip took, but you don't know how many gallons were consumed to travel that distance. If you are suggesting that the octane rating of each tank of gas greatly influenced your miles per gallon you can't use a "tank" as your unit of measurment. Heck at only 13 miles difference in trips, I suggest wind or you were driving down hill during one of the trips is the difference in 13 miles. A "tank" is not a unit of measurement! Haven't we had this discussion?

  6. #81
    EChas3's Avatar
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    Re: Gas Mileage

    Octane is a measurement of anti-knock qualities not energy content.

    Higher octane gas will allow the ECM to advance the timing and produce more power under load but in my experience with the gas around here, the mileage at a steady cruise is the same.

    Literally, YMMV!

  7. #82
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
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    Quote Originally Posted by malatu

    That means absolutely nothing unless you know exactly how may gallons it took to travel the mileage you recorded. Remember, the benchmark that is use to determine the efficiency, is miles per gallon, not miles per tank!

    So there was a difference of 13 miles beween the two trips. You know how many miles each trip took, but you don't know how many gallons were consumed to travel that distance. If you are suggesting that the octane rating of each tank of gas greatly influenced your miles per gallon you can't use a "tank" as your unit of measurment. Heck at only 13 miles difference in trips, I suggest wind or you were driving down hill during one of the trips is the difference in 13 miles. A "tank" is not a unit of measurement! Haven't we had this discussion?
    My post was relevant to a previous poster's comment regarding the change of octane making some difference in the mileage. Was just sharing that. Now, as far as mpg (which was not my intensional to convey), the trip going up was 293 miles, and I put 15.2 gallons in when I filled up there with 87 at BP in prep for the trip back.

    And yes the discussion was had before.

  8. #83
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    Re: Gas Mileage

    I can see we are ate the circular reference syndrome here.

    here's a bit i was able to determine.

    My Northstar - without the cruise control, at 75 MPH maxed out at approx 21.5 MPG avg over a 30-40 mile segment of interstate.

    With the adaptive cruise control finally fixed (Yay!!!) MPG went to 23.5 average on the same stretch of interstate with a few instances of cars cutting in front of me making the acc slow the car down & then speed back up. I don't think it would get any more than about 0.2-0.3 MPG better on a complete open road though.

    A 2011 V6 STS (rented) on the same stretch of road with non-adaptive cruise got approx 26.5 MPG at 75 MPH average speed.

    I'll try it again tonite. I hope the road is not too crowded.

  9. #84
    EChas3's Avatar
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    Re: Gas Mileage

    To preserve your deja vu, the DIC cannot be assumed acccurate.

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