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MPG descending while breaking

Discussion in 'Gen 2 Prius Main Forum' started by Motorway, Feb 4, 2006.

  1. Motorway

    Motorway New Member

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    Curious why sometimes I'll be coasting/breaking to a stop and the display will show 99.9 all the way to the end, and then other times I'll get the gradual drop from 99 to say 68.5, then 32, 16.5, down to zero.

    I haven't noticed any difference in what's going on with the engine in those separate instances, but I've only had the car for one week, so not entirely in tune with the vehicle yet.
     
    #1 Motorway, Feb 4, 2006
  2. SomervillePrius

    SomervillePrius New Member

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    I see the same thing in the beginning. I take it to mean that the engine (ICE) is running and as you slow down the ICE continues to run at the same RPM (to heat up the engine and catalystator). The effectivley cuts your effective MPG down. This is why it's good the more you can drive in the beginning since the ICE will run to get warm (and use quite a bit of gasoline doing it) so you might as well try to make use of it.
     
    #2 SomervillePrius, Feb 4, 2006
  3. EricGo

    EricGo New Member

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    I see it every day, since the first mile of my drive is downhill.
     
    #3 EricGo, Feb 4, 2006
  4. SomervillePrius

    SomervillePrius New Member

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    yeah me to, but I need to coast into red-lights :-(
     
    #4 SomervillePrius, Feb 4, 2006
  5. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    There are two ways to come to a stop: with the ICE off and with the ICE on.

    If the ICE is off before you start decelerating, it will most likely remain off and you will see 99.9 until the end.

    If the ICE is on when you sart decelerating, it might or might not shut down before you come to a complete stop. In the case you explain, it does not. (If it did, of course, you would see 99.9) It's possible - and has been discussed on this board - that the ICE can operate and you can still have a at-the-moment reading of 99.9 MPG for that given speed. However, as you slow down, you cover less distance while consuming the same amount of gas. With that in mind, it's simple math to see that your MPG will decrease until you are covering no ground and the ICE is still running. But, you say, the ICE is off when I'm standing still. It's a tricky one; we've all been fooled by the sneaky ICE.
     
    #5 TonyPSchaefer, Feb 4, 2006
  6. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    yep when ICE is cold, its common to see regen being sent back to the battery only and still have as low as 15 mpg. here is an example

    http://priuschat.com/forums/album_pic.php?pic_id=753

    oops...make that 13 mpg...sorry for the fuzziness... it was taken at 4:30 AM. now i realize that this pic was first posted to PriusChat on August, 13, 2004... a Friday.. but this is no joke. but is kinda scary...but rest assured, it is completely normal
     
    #6 DaveinOlyWA, Feb 4, 2006
  7. Motorway

    Motorway New Member

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    Damn sneaky ICE!

    Thanks for the informative posts, everyone. I'm learning more every day.
     
    #7 Motorway, Feb 4, 2006
  8. V8Cobrakid

    V8Cobrakid Green Handyman

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    hehe.. seems like normal engine warm up. sometimes you can trick the engine into an early shut off by switching to Neutral then back into D. I used this a lot in Colorado when it was only 15 Degrees out. I also kept my A/C. off though.
     
    #8 V8Cobrakid, Feb 4, 2006
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