Fantastic gas mileage on highway trip - 2008 DTS
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Cadillac DTS Forum - 2006 through 2012 Discussion, Fantastic gas mileage on highway trip - 2008 DTS in Past Cadillac Vehicle Discussion; My car got 33 MPG on my trip to and back from Alabama this weekend. I was by myself and ...
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    rebel7254 is offline Cadillac Owners Member
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    Thumbs up Fantastic gas mileage on highway trip - 2008 DTS

    My car got 33 MPG on my trip to and back from Alabama this weekend. I was by myself and not carrying a heavy load or anything, but I still think that's pretty remarkable.

    I know part of the reason for the great mileage is the fact that I put ethanol-free 93 octane gas in it. This makes a noticeable difference just driving around home, getting me 20 MPG instead of 17 MPG that I get with 10% ethanol 87 octane. But 33 MPG on the highway is a huge jump that I did not expect.

    I also kept it at 65 MPH on the interstates, which helped I'm sure. I like that speed not only for the better fuel mileage but because it's just more relaxed since you don't have to worry about passing nearly as much.

    I know there's debates about how much advantage you get by putting the ethanol free and/or premium gas in these engines, but I can attest at least in my own experience that it makes a significant difference. Yes, the price per gallon is going to be more, but I've done the math and in my area getting 20 MPG instead of 17 MPG makes up for the price difference. The cost per mile ends up being about the same.

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    Superjim's Avatar
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    The only way mine would ever get 33 mpg is if I was going downhill all the way... LOL

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    Submariner409's Avatar
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    rebel, You need to contact Cadillac and the EPA - you'll be an instant millionaire, considering the CAFE figures for your car are:

    EPA - City = 15 mpg; Combined = 18 mpg; Highway = 23 mpg.

    That you were able to see a 33% increase in highway mileage in this car is truly revolutionary.

    I drove to Charleston, SC on Shell 87 E10 over Thanksgiving. I drove back using Shell 87 straight gas. No mileage difference - none. None. (and running Shell 93 makes so little fuel use difference it isn't worth mentioning - but, yes, it adds considerably to the mileage cost.)

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    SCDTS is offline Cadillac Owners Member
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Just some thoughts and comments. Did you calculate this mileage or take it off the dash computer?
    All the Cadillacs I am familiar with have had very accurate computer readouts - gallons used to pump readouts gives accurate mpg (2 Chevrolet computers give less used than pump fill-up and high mpg on computer vs actual/calculated). I have found on trips from SC to West TN using Hi test and my foot to control the cruise I have gotten 24- 26(best for trip one way - about the same both ways), but not as great as yours.
    Congratulations. Keep it up

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Yeah, I'm sorry but I don't believe it. The entire trip had to be downhill with a strong wind. For my area, there is no better test than the AC Expressway and the best I've ever been able to do is 26 and that's cruising at 55 mph, no wind, no traffic, perfectly straight road.

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    Superjim's Avatar
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    The best mine has EVER got is 24... and that's driving REAL EASY...
    Normal mileage for my car... on the highway... is 20/21....

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Meanwhile, in my daily trip back and forth to the office (4 miles each way, all back roads) I average 13.5 mpg which kinda sucks.

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Quote Originally Posted by StuJac View Post
    Meanwhile, in my daily trip back and forth to the office (4 miles each way, all back roads) I average 13.5 mpg which kinda sucks.
    I get 16/19 here in town...(as long as I don't STAND ON IT very much)... but most of my driving is on the freeway...

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    That's the difference, the freeway. I'm on the freeway on Saturday's, on the way to dinner. Every other month to Atlantic City and that's about it.
    Superjim likes this.

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Just did a 80 mile round trip up north on 50 mph roads. Went thru a couple of towns. DIC said 8.7 liters per 100 km. which is 27.5 mpg U.S. gal.
    I have not checked fill up to fill up as I like the DIC numbers.
    Norm

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Norm you just nailed the issue: it's the axle ratio that makes the difference between you and Superjim. I too get great mileage out of town especially on the flat bits - up to 34 mpg (Imperial) and that is because we both have the Lux III, not the Performance model like Jim.

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    Superjim's Avatar
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    Quote Originally Posted by hazcaddy View Post
    Norm you just nailed the issue: it's the axle ratio that makes the difference between you and Superjim. I too get great mileage out of town especially on the flat bits - up to 34 mpg (Imperial) and that is because we both have the Lux III, not the Performance model like Jim.
    Maybe a combination of axle ratio and my big foot... LOL LOL
    Also remember that freeway speeds here in Fort Worth ( not counting rush hour) are usually around 75mph and interstate speeds in Texas (once you get out of town) run around 85..
    That's not a good way to get good mileage...

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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    IF these later "DTS" cars have 2 different final drive ratios - 3.11:1 economy; 3.71:1 performance - then there is a 2 - 4 mpg difference in highway gas mileage.

    It is not uncommon to see 26 - 28 mpg open highway in the 3.11 cars, 24 or so in the 3.71 cars. In town or near suburban it takes gas to accelerate 4,000 pounds and the final drive ratio factors less into that type of mileage.

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    rebel7254 is offline Cadillac Owners Member
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    Re: Fantastic gas mileage on highway trip - 2008 DTS

    The trip computer has a gallons used measurement, which I reset at fill-up. I also reset the "Trip A". Then when I'm at the station to fill up, I take the miles on Trip A and divide by the gallons used. Finally I compare the gallons used with how much the pump says I put back in the tank to fill it up. It is always within a half-gallon.

    I understand the doubters, but it is what it is.

    I'm looking at my receipt right now from where I filled up in the town I was leaving. I put 12.61 gallons in the tank. According to Google maps, the route I took home was 438 miles. I did not have to stop to fill up again.

    438 / 12.61 = 34.73 mpg

    By the time I filled up again, I had driven probably 30 or 40 miles "normally", so that could have taken it back down to the 33 figure.

    Y'all don't have to believe me, that's fine. Doesn't bother me a bit. I'm taking my wife and son to Myrtle Beach in September. I'll report back here on what kind of mpg I get. I don't expect to do as well because:

    a) I'll be hauling significantly more weight.
    b) We'll have to climb the mountains in I-26 in Northeast TN and Western NC.
    c) We might be traveling with my in-laws (separate vehicles) and my father-in-law won't want to go 65 mph.

    ----------

    Quote Originally Posted by Submariner409 View Post
    rebel, You need to contact Cadillac and the EPA - you'll be an instant millionaire, considering the CAFE figures for your car are:

    EPA - City = 15 mpg; Combined = 18 mpg; Highway = 23 mpg.

    That you were able to see a 33% increase in highway mileage in this car is truly revolutionary.
    Why would it make me a millionaire? You think they'd give me a million dollars to study my car or something?

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    You don't always end up with the same amount if fuel when you "fill up", and you don't always fill up with the same amount of fuel remaining, so that's not an accurate way to track mileage at all. Google Maps distances are also not always accurate.

    The MPG readout on the DIC uses the exact distance driven, and the exact amount of fuel that is injected to reach its number, THAT is accurate.

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