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Cadillac STS Forum - 2005 through 2012 Discussion, Gas Mileage in Past Cadillac Vehicle Discussion; I get ABSOLUTELY HORRIBLE gas mileage. $60 gets me about 215 miles around town (inner interstate and beltways mostly). And ...
  1. #1
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
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    Gas Mileage

    I get ABSOLUTELY HORRIBLE gas mileage. $60 gets me about 215 miles around town (inner interstate and beltways mostly). And not a hell of a lot more on long trips. And I've noticed no mileage difference between using 87 and 93 from Shell and BP. Way different from my 99 STS.

    Can it be better? It's all tuned up and running great. And I'm not driving it hard constantly.

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  3. #2
    ddalder's Avatar
    ddalder is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    Well, you're doing better than me! I attribute some of my poor gas mileage to extra idling in the winter and remote starts. I know mine will improve with warmer weather, but it's extremely poor right now.

  4. #3
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
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    I've heard so many things, some people say it's because it is four-wheel-drive. Others are saying it's because it's a V-8. Then others even say that it's because of the gearing in the car.

  5. #4
    chazglenn3's Avatar
    chazglenn3 is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    It is the sum of those parts...AWD, V8 and 3.23 gear ratio equals a bad ass car that gets mediocre mileage. You bought a luxury performance car...not a Prius.

  6. #5
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
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    I was looking forward to 17 city and 25 highway.

  7. #6
    ddalder's Avatar
    ddalder is offline Cadillac Owners Connoisseur
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    Re: Gas Mileage

    I'm not looking for gas mileage that will compete with a Prius, but I did expect better than what I've seen lately. Of all the cars I've ever owned, only one wasn't a V-8 so the world of bigger, more thirsty engines isn't new to me. The past few fills, I've been getting barely more than 125 miles to 14.5 gallons. I have no driveability problems with my car. The intake is snug, tires are properly inflated, other maintenance is up to date and I have less than 40,000 miles.

    Compared with my 4.6L Northstar Bonneville, the STS gets about half the fuel economy. I understand it's a different configuration, somewhat different engine etc, but this is a big variance.

  8. #7
    AkeenWash is offline Cadillac Owners Member
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    Man I just purchased a 95 edlo northstar and I changed the oil and air filter, checked tire pressure, got a tune up, checked everything and I still barely get 11 mpg!!!-___- is there anything else I can do?!

  9. #8
    KRSTS is offline Cadillac Owners Enthusiast
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    Re: Gas Mileage

    Quote Originally Posted by maiahsdad View Post
    I was looking forward to 17 city and 25 highway.
    That is what I get on my 08 RWD 3.6DI.

  10. #9
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Gas Mileage

    The biggest factor in gas milage is the weight of the driver's foot on the gas pedal. Set the DIC for instantaneous milage and you'll see where the gas is going.
    Don't mess with Binky Bear!


  11. #10
    mckellyb is offline Cadillac Owners Enthusiast
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    Re: Gas Mileage

    Really poor MPG, but no obvious problems, typically means an oxygen sensor is failing or is totally hosed.

    When these die, the engine's computer defaults to full-rich 100% of the time.

    Sure, the car should tell you there's a problem, but I've seen bad O2 sensors not tip off the ECU.

    Don't forget, winter, "oxygenated" fuel has less actual gasoline in it, more air, so you'll see a 10-20% drop, depending on the vehicle.

    This annoys me to no end, because the reason behind it, old cars with stuck chokes, are not a common daily-driver any more. This was the reason it was introduced.

  12. #11
    Smiling Jack is offline Cadillac Owners Fanatic
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    Re: Gas Mileage

    Quote Originally Posted by AkeenWash View Post
    Man I just purchased a 95 edlo northstar and I changed the oil and air filter, checked tire pressure, got a tune up, checked everything and I still barely get 11 mpg!!!-___- is there anything else I can do?!
    Akeen,

    I had a '95 Seville STS with the Northstar V8 for 13 0r 14 years. I never got less than 28 to 30 mpg on long highway trips, but I never usually got more than 10 or 12 mpg in our regular city driving. The reason was that our usual daily trips were less than 5 miles. When on occasion I did a daily trip of 12 or 15 miles (one way), I would get 15 to 20 mpg. Short trips kill mpg because it simply takes a certain extra bit of gasoline (perhaps one or two tenths of a gallon depending on outside air temperature) to warm up a cold engine, and unless you drive a long enough distance to average that out, you simply can't get up to normal average mpg.

  13. #12
    maiahsdad's Avatar
    maiahsdad is offline Cadillac Owners Fanatic
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    Quote Originally Posted by Smiling Jack

    Akeen,

    I had a '95 Seville STS with the Northstar V8 for 13 0r 14 years. I never got less than 28 to 30 mpg on long highway trips, but I never usually got more than 10 or 12 mpg in our regular city driving. The reason was that our usual daily trips were less than 5 miles. When on occasion I did a daily trip of 12 or 15 miles (one way), I would get 15 to 20 mpg. Short trips kill mpg because it simply takes a certain extra bit of gasoline (perhaps one or two tenths of a gallon depending on outside air temperature) to warm up a cold engine, and unless you drive a long enough distance to average that out, you simply can't get up to normal average mpg.
    I drive 19 miles each way every day.

  14. #13
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Gas Mileage

    Until the engine warms up it operates in open loop where the ECM uses a look-up table to set the mixture rather than responding to the O2 sensors. Short trips in cold weather kill milage and it takes a lot of driving after the engine warms up to bring the overall milage back up. If you look at the original window sticker, there is a $1500 charge for gas guzzler tax with good reason; it's a gas guzzler.

    The best you can do is keep a light foot on the go-pedal and keep the speed down.
    Don't mess with Binky Bear!


  15. #14
    ddalder's Avatar
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    Re: Gas Mileage

    That is RPO:

    R8E - GAS GUZZLER TAX

  16. #15
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    Re: Gas Mileage

    I'm at the opposite end of the spectrum. I commute 8 miles one way to work. And really don't put much other mileage on the car. i averaged 18-20 most of the time. When we did take it on a road trip to CA, I was averaging around 25-28. Overall pleased. Considering the 2002 VW Jetta with the 2.8VR6 i used to have got worse mpg's then this and didn't have 300hp.

    matt

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