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Cruise Control and Poor MPG?

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    So I decided to take my tC on a road-trip to Portland, OR from SLC, UT. I measured my MPG by dividing the trip counter by the gallons of gas filled up at every pit-stop. There was a segment (somewhere in the middle of Idaho) where I predominantly used cruise control at 74~75mpg. I got about 23-24 MPG, which seems AWFULLY low for highway mileage in an automatic tC.

    Here's the catch/disclaimer, I did have my snowboard on top of my yakima rack. Mod-wise, I just have the rear-sway + front-strut bar combo, aFe Pro Dry s drop-in filter. I suspect that the snowboard is causing my MPG to drop.

    At 65 mph my rpm's are about 2.5k-2.6k, at 75mph they are slightly under/around 3.0k; does that seem normal? And if so, who are these people claiming at 3.0k rpm's they can get 29-30mpg? Anyways the last factor I could see throwing my numbers off is the presence of hill, when the computer would shift down aggressively to maintain cruise-speed. (Or maybe I just "forgot" about segments where I was jumping out of cruise-control to pass people for fun...)

    Thoughts anyone?
    I have an automatic as well and the rpm seem to be the same as mine. I was checking my mpg the other week and ended up getting around 29mpg going 75-80 highway driving(I thought it a little high but the numbers didnt lie). I have an injen CAI and a lightweight crank pulley. Im not positive but I would not think a snowboard would cause enough drag to drop the mpg that much as well.
    • Edited 1 times, last by libtech on .
    Good to hear about the RPMs. Also just a FYI I just barely got my 2nd free quick-lube (~8300 miles) at the local dealership the day before I drove out.

    EDIT: Oh and you have to add the ski-rack too. That thing makes opening the sun-roof sound like a wind-tunnel...
    I noticed the SAME thing...

    Using the Cruise Control...my MPG's have gotten worse vs. driving with a Lead Foot.

    Hmmm....

    Thought Cruise Control suppose to "improve" MPG's......
    UltiMica06 wrote:
    Using the Cruise Control...my MPG's have gotten worse vs. driving with a Lead Foot.



    Maybe our feet are full of legendary driving skills... Do you by any chance have hills where you drive lots? I'll measure it again on my way back down from Portland, and maybe stash the snowboard in my car.
    I was using cruse control and my car has right over 65000 miles. I have noticed that the mpg has for some odd reason seemed to increase as the car goes up in miles. I dont know if there is any real truth to that though.
    I go back and forth with cruise and my foot during my weekly road trips and I get 29-31 easily.
    Just to let you know that when you drive like past 55mph your losing good gas mpg even if your in cruise or not. The difference between 75mph and 55mph theres a good 15-20% difference in gas consumtion. try crusing at 55 and compare it to your 75 youll notice a difference and ig you dont..well then its something else lol
    It seems like you answered your own puzzle:

    Cruise control uses the least amount of fuel in the most efficient manner possible, it is a computer controlled function that cannot be duplicated by the human foot pressing the pedal.

    If more fuel is used on the highway trip, its not possible for cruise control to be the culprit.

    You mention the board on top of the rack, which actually can cause a difference in car aerodynamics, much more so than having the windows rolled down.

    Extreme wind and disturbed aerodynamics can reduce fuel economy by as much as 20%

    one more factor likely to cause a slight drop in fuel economy is weight: even 100 lbs is enough to change your economy

    add the factor of weight and wind dynamics at 75 mph and you get a recipe for reduced economy
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