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Driving up hill and MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Jellopy, Dec 8, 2009.

  1. Jellopy

    Jellopy New Member

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    I live in salt lake city and my workplace is just 7 miles away with some stop signs
    and traffic lights. I drive up hill a lot to my workplace.
    My MPG is suffered from my up hill driving. I drive in ECO mode all the time and
    I got around 30-35 MPG on average while you guys got 45+ MPG
    I have tried glide driving but it doesn't do much while up hill
    Any suggestion? Thank you in advance.
     
  2. ken1784

    ken1784 SuperMID designer

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  3. qbee42

    qbee42 My other car is a boat

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    You should also gain some back on the downhill drive home.

    Your main "problem" is your short drive to work. Seven miles is short enough that you take a major hit warming up the engine each time. On the other hand it's great to have a short commute.

    Tom
     
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  4. SageBrush

    SageBrush Senior Member

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    Qbee is right. An EBH would prewarm the engine for the morning commute; grill blocking might keep the engine warmer than not by the time to go home.
     
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  5. bwilson4web

    bwilson4web BMW i3 and Model 3

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    You might treat this as an experiment and start gathering some data and comparing the results:

    • temperature and tripmeter to work - all three variables, distance, MPG, average speed
    A ) No warm-up - get three samples

    B ) Warm-up in driveway to engine off (make sure car in ECO and heater is off during warm-up) - get three samples

    C ) Alternate route(s) to work - three samples

    D ) Alternate max speeds to work - three samples

    You'll have the car for a long time so experimentation is good. Better still, share your results.

    Bob Wilson
     
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  6. Jellopy

    Jellopy New Member

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    From my experience, if I reset trip A (I use trip B as life time MPG) From my home to my workplace (uphill) I got about 30 MPG and I reset my trip, again on my way back home (downhill) I got about 70-80 MPG. Surprisingly when I continue drive my trip A in 1 week I got only 35 MPG combine and now it's 10-15F here in salt lake city. I can't drive with out heater. I guess that's why my MPG suffered so much.

    Thank you for all replies, I will keep doing my experiment.
     
  7. ken1784

    ken1784 SuperMID designer

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    You can't do a simple mpg averaging here.

    It looks a little inconsistency in your numbers, but if numbers like this, it is not 45mpg average.
    miles mpg gallons average-mpg
    1 7.0 25mpg 0.280
    2 7.0 65mpg 0.108
    3 14.0 0.388 36.1mpg

    If you saw these numbers on your commute, you consume extra 0.086 gallons for uphill and you gain 0.086 gallons for downhill.
    Reflecting the 0.085 gallons per 1000ft rule, I can guess your altitude change is 1013ft. :)

    Ken@Japan
     
  8. Jellopy

    Jellopy New Member

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    Wow... I see the calculation now, Thanks for clarification Ken.
    I'm always wonder why my MPG was so low. The MPG gain from downhill drive didn't
    give much benefit then. I'm not sure what is my altitude change but I know it's
    quite high due to I have to drive in power zone so many times to keep traffic flowing.
     
  9. F8L

    F8L Protecting Habitat & AG Lands

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    Yup, they covered the calculations for you. :)

    I used to routinely avg. 52mpg when I had a normal highway commute on flat ground but once I switched jobs and went from a 76mile commute (flat ground) to a 13mile commute (over 1,000ft. elevation gain) I dropped down to mid-high 40s. :(
     
  10. ken1784

    ken1784 SuperMID designer

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    I bet it's caused by 7 miles short commute.

    Ken@Japan
     
  11. KV55

    KV55 Member

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    I have an 8 mile commute going from 40m to 110m altitude, and have found that blocking the grill does give me 3mpg UK better results during the winter months, that said it isn't so cold here (8C today) and I can cycle two or three days each week so avoiding the short journey completely. I get 45 to 50mpg UK inbound and 65 to 70 outbound. I do like the information given by Ken about the fuel needed to gain altitude, very nice, thanks Ken. Anyone have any thoughts of trying to get back, being downhill, on the battery alone, but then the cabin will be a bit too cold? I wonder if the downhill stretch will yield more improvement.
     
  12. kgall

    kgall Active Member

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    KV55, I love the combination of Miles traveled, Meters of altitude, Celcius temperatures and UK gallons in your post.

    For the whole gang, especially the techies,
    My father told me that accellerating up hills was bad for mileage. Is this true?
    Now, Ken tells us that a certain amount of gas is required to lift a given weight a given amount--i.e., to increase its potential energy. I take it that this reasonably disregards the higher amount of the vertical component of wind resistance on the car when the slope is steeper or the speed is higher.
    When the weight drives back down, some of the potential energy is lost, again to wind resistance, which is one reason why regen on downhill doesn't capture all the additional energy used to drive uphill.
    So, obviously, I'm forgetting some basic physics formulas about the energy use of uphill accelleration???

    And my ultimate question is this: better for gas economy given the toyota hybrid system to accellerate uphill, go at a steady pace uphill, or slow down uphill?
    Where should I try to keep the hybrid system indicator (if that is relevant at all)?
     
  13. bwilson4web

    bwilson4web BMW i3 and Model 3

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    No because it puts the engine in higher power, regions, decreased engine efficiency. It isn't as bad with the 1.8L engine due to cooled exhaust gas recirculation compared to the 1.5L Prius but it is observable. This is especially true if running 87 octane and not 89:
    [​IMG]
    Ok but still tends to get in the higher power regions and can 'over drive' the gasoline octane.

    Depends on traffic. If you can use a truck as your pacing vehicle, DO NOT TAILGATE, you'll be in good company going up the hill.

    Hills come in many grades and weather conditions are often different. The cooled exhaust gas recirculation has made things less bad but my personal experience is once the HSI is 'pegged', engine rpm is the only indicator left. I agree with Hobbit that a little gap on the end of the HSI "PWR" bar makes sense but mostly I like to either keep the speed constant or let it bleed off say 5 mph or just use a truck as the pacing vehicle up the grade.

    If you're driving often in hilly areas, try 89 octane. The 1.8L engine can exploit the higher octane to improve climb efficiency.

    GOOD LUCK!
    Bob Wilson
     
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  14. Celtic Blue

    Celtic Blue New Member

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    Hills with stops and short commutes are a tough combination. You don't recoup the potential energy on the downhill because of the stops. The ICE will run needelessly going downhill while the engine is warming. Plus each of the stops results in inefficient transfers back and forth to the battery.

    Add in cold weather and you really take a hit.

    About the only advantage of hill climbs is that one during the warmup will bring the ICE to temperature quickly.
     
  15. F8L

    F8L Protecting Habitat & AG Lands

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    I agree mostly Shawn. I have a short 13mile commute starting at approx. 200ft elevation and I drive less than 1 mile to the freeway and only 3/4 of a mile off the freeway till I get to work which is at approx 1,220ft. elevation. I watch my Scangauge and on cold days (40deg or less) I do not reach full operating temperature till I'm nearly at work (70mph avg.).

    On the way home I try to coast as much as possible while maintaining 70mph avg. and I find that the car doesn't reach operating temperature until I'm back off the freeway and go through a couple stop lights but then I'm home. lol

    Like you stated though, I never recover the mileage I lost from going uphill. I tested this the other day get about 55-60mpg downhill and about 25-28mpg uphill (27deg uphill, 38deg downhill). I'll test this out in the really hot summer months since this will add about 60-70deg to ambient temperature.
     
  16. tumbleweed

    tumbleweed Senior Member

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    I need to remind myself that if I go up and then down a hill using the same route my overall mileage will always be less than twice what I got going up.