Better MPG's Coasting?????

Discussion in 'Performance & Fuel' started by Enkeiavalanche, Jul 23, 2011.

  1. Enkeiavalanche

    Enkeiavalanche Rockstar 4 Years ROTM Winner 5000 Posts

    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?

  2. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    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.
  3. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    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.
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    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?
  5. Enkeiavalanche

    Enkeiavalanche Rockstar 4 Years ROTM Winner 5000 Posts

    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. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    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!!
    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. stephan

    stephan Rockstar 4 Years 5000 Posts

    Makes sense now Charlie.

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