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  1. #1
    Legend


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    Default Better MPG's Coasting?????

    So anyway as I go to work in the morning there is a mile long hill I go down on Rt80. So most of the time I am going between 65-70 mph and I can coast the whole way down..I see about 99mpg on the DIC and it's in 4 Cyl mode. The other morning I had the AC on and it would only go to 77MPG as soon as I turned off the AC it went back to 99MPG....

    What do you think?

    08 Z71 Avalanche Mods to date: K&N CAI,Hellwig Swaybars and End Links, Corsa Sport Exhaust, Superchips Programer,IPCW LOF & 3rd brake light and tails, AMI Gas door,Show Hooks and Door locks, Enkei Wheels, with Pirelli tires, StreetScene Bowties, Grant Steering wheel,Muth signal mirrors,SSBC Big Brake kit,Huskyliner Mug gards,Floor mats and Hood shield, McGard Lug nuts and locks, Bedrug, Cervini's Ram Air hood,35watt HID Fog lights, Sylvania bulbs all around ZXE's Highs and Lows, WhiteNight Back up lights,Sirius and HD Radio, SnugTop sitting on deck now Got a Softopper on now,Tempress Boat Hatches.... New Bilstein shocks are on... New Mods coming soon..... X

  2. #2

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    I think that maybe the best way to dramatically improve gas mileage is to always drive downhill.

    I expect the difference is either related to the additional drag created by the AC system, or something in how the DIC calculates MPG.
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    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  3. #3
    Legend

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    Default

    On my 1998 2wd Suburban 1/2 ton- my Scangauge shows .7gph idling with the AC on, but .6gph with the AC off-so
    your 99mpg vs 77mpg seems about right.
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  4. #4
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    Default

    Wow that's about a 23% loss from the AC. Seems like something else is also comeing into play here. Was the weather different on those two days Enkei?
    1988 Chevy C-3500 2wd (no pic)
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  5. #5
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    Default

    Nope.. Same hill same time as I go down it changes when I turn on or off the Ac. I can be going down the hill and turn on the AC and it goes from 99-77 right away..I know it runs on the same belt and all but that much in 2 feet?

  6. #6
    Legend

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    Stephan-I can buy the 23%-my 5.7 uses about 17% more- his more efficient "4CYL" will use a higher percent to run an extra load-the AC
    Pretend the 5.3 uses 1 gph to idle-no ac(it doesn't- it probably uses .4gph in 4 cyl mode)
    Pretend My 5.7 uses 2 gph to idle- no ac(it actually uses .6gph)
    BUT THEY PROBABLY USE THE SAME EXTRA .1GPH to run the ac.(my gadget says mine uses .6gph no ac- but .7gph with ac- idling-stopped)-
    Your more efficient vehicle uses-1.1 gph and extra 10% to run the AC
    My less efficient uses 2.1gph-extra 5% to run ac.
    The above numbers are just pretend numbers
    My actual numbers are .6gph no ac and .7gph ac-17% or so
    The better a motor is the "worse" it looks" when extra loads are added.

    Hey how would you like to make a STRAIGHT UP trade for a genuine 1998 LS Suburban-5.7 2wd- with JUST 216,400 MILES??I could manage to "LIVE" with your Avalanche-HA,HA!!
    Didn't think so!!
    Charlie
    PS Up on my roof for me now-our drought lifted-south Louisiana- about 4 weeks ago-
    Our 24 yo roof leaking like a sieve- broke for another 19 months(62yo SS) so having to do cheap out "repairs". Maybe I'll luck out and get full time work!! Sub teach now $62/d.Roof materials maybe $3000-guess in 25 months I'll be learning how to DIY a roof!!




    My point- finally- is the less a motor uses at idle(more efficient it is-like your cyl shutdown 5.3) the bigger the drop in mpg will be if you turn on the AC.
    I can buy the AC making that big- 25% a difference idling/coasting.
    FYI coasting downhill at 60 mpg my 5.7 will show no higher than 50 mpg I think

  7. #7
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    Quote Originally Posted by phoebeisis View Post
    I can buy the 23%-my 5.7 uses about 17% more- his more efficient "4CYL" will use a higher percent to run an extra load-the AC

    the less a motor uses at idle(more efficient it is-like your cyl shutdown 5.3) the bigger the drop in mpg will be if you turn on the AC.
    I can buy the AC making that big- 25% a difference idling/coasting.
    FYI coasting downhill at 60 mpg my 5.7 will show no higher than 50 mpg I think
    Makes sense now Charlie.

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