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Going downhill at 70-80 mph

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Deoc, Feb 20, 2019.

  1. Deoc

    Deoc Member

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    The engine will start at abou 65 mph even if going dowhill on ev mode, what would be the best way to save gas?sometimes im driving downhill at 70-80 mph for 2-3 miles but the engine stays on, slowing down to less tha 65 mph seems to upset a lot of drivers, does the engine still uses gas or is the engine using the car momentum ?
     
  2. Pluggo

    Pluggo Senior Member

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    With a Scangauge II or a similar device in your OCD-II port you can see the actual (alleged) engine-load in real time. Personally, I never hit 70 mph. It's a Prius, people are not going to like you anyway.
     
  3. 4est

    4est Active Member

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    No engine uses has when doing engine breaking. No modern ones, at least. Old carb engines did use

    So, don't worry about it
     
  4. QuantumFireball

    QuantumFireball Active Member

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    I think the engine will use some fuel during the startup cycle, it won't be just doing engine braking in this phase as it needs to get up to temperature (to heat up the cat, etc.)
     
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  5. jerrymildred

    jerrymildred Senior Member

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    If it's using any gas at all in that scenario, it's miniscule. I think the only way to save more is with a pure BEV or maybe a Prime.
     
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  6. gallde

    gallde Active Member

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    The ICE has to turn (for power OR braking) when above 65 M/H because otherwise the MG would over-rev.
     
    Yea Right, fuzzy1 and jerrymildred like this.
  7. Deoc

    Deoc Member

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    I will make a test next time i get a chance, i think maybe resetting the odometer just when i start going downhill and see if the mpg goes down, usually in ev mode says 999 and if going downhill with the engine on and i see the mpg goind down then i would think is using gas?
     
  8. mpg_numbers_guy

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    Not necessarily. If the engine is running downhill while braking the engine alone will be using so little fuel that it itself will be exceeding 99.9 MPG.
     
  9. Deoc

    Deoc Member

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    Not sure how the car calculates mpg, I thought maybe it calculates the mpg by calculating distance and fuel use.
     
  10. QuantumFireball

    QuantumFireball Active Member

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    I'm not sure it actually has a fuel flow meter? They are a relatively expensive component, so trip computers are usually calculating based on airflow and other data - hence they're not the most accurate things around.
     
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  11. jerrymildred

    jerrymildred Senior Member

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    I've read in other places that that's how it works. Ut's just inferred from other data, as you said.
     
  12. Deoc

    Deoc Member

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    I would think that mabye it uses the injectors information to calculate mpg as those are the ones injecting gas but not sure about that, I bought bluetooth adapter and as soon as i get a chance i will go ahead and test it
     
  13. Deoc

    Deoc Member

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    For those that wonder about it, I made a test going downhill about 2 miles, I reset the trip just when I started going downhill and I made sure it stayed on "chg" the mpg was 999, there was significant drag even when I tried to keep the"chg" as low as possible, so it seems like the motor uses the car momentum to keep going without actually using any gas, as soon as I pressed the pedal slightly the mpg went to 453, even when the motor is not using gasoline is creating significant drag on the car so in order for me to keep up to the speed everyone else is going even going downhill I had to slightly accelerate thus using gasoline.
     
  14. fuzzy1

    fuzzy1 Senior Member

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    Keep in mind that there is no legal 75 or 80 mph anywhere in Washington, 70 is the highest legal limit for cars. In my corner of the state, there are always some cars staying legal.

    And 60 is the highest legal limit for trucks. And a few trucks even obey it, even on downhills. And more will keep down to your Pip's MG1-imposed ICE-off speed limit. Can you find and stay behind some of them? Many drivers upset with slow isolated Prii, suddenly switch lanes and try to beat them around the slow truck just ahead. This is often a convenient way to go slower and shake those folks who think you should go faster.