50MPG Mountainous Commute

Discussion in 'Gen 2 Prius Main Forum' started by John Dadmun, Jun 1, 2021.

  1. John Dadmun

    John Dadmun Junior Member

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    It makes no sense that I would get 52.8 mpg considering the mountainous commute that I have, 21+ miles each way, every day. Could my Prius 2nd gen 2009's mileage figures, be incorrect? Considering the rest of the vehicle and the outstanding engineering exemplified in the design, I rather expect the cars reported mileage figures to be correct. With a sample of one, I can only know for myself.
     
  2. oldtechaa

    oldtechaa Active Member

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    Doesn't sound at all unbelievable for a Prius in good condition. The 21+ mile commute and the hills can actually help to warm it up.
     
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  3. PriusCamper

    PriusCamper Senior Member

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    MPG has alot to do with temperature and gas quality. As we get into warmer weather engine MPG goes up, as well as Summer gasoline makes for higher mpg.

    But the very best way to ensure max MPG when it comes to hill climbing is using an OBD2 bluetooth adapter and a free phone app, like "OBD Auto Doctor" so you can monitor engine RPM and keep it at 3500 RPM when climbing the steep stuff. Here's my phone screenshot when I was climbing up out of the Sacramento Valley into the mountains of S. Oregon last week. I got best hill climbing MPG ever with this technique.

    Screenshot_20210528-215607.png
     
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  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Out of the 3 generations we've had (Gen 2, 3, 4/Prime), I recall the Gen 2 being the most accurate.

    I suppose it's possible. I've gotten 60mpg (3.9L/100km) over an entire tank (826km... about 512 miles) that included a trip up and down a small mountain (university at the top of said mountain)
     
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  5. John Dadmun

    John Dadmun Junior Member

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    I really wonder about regenerative braking, I use the B mode to scrub off speed on any hill, but there are some steep hills where that B gear's resistance isn't nearly enough - if I apply just a light and constant touch to the brakes, will that then transfer more regenerative power to the HV battery, for a short time, than the B gear would alone?

    I saw on a youtube video, someone said that B mode runs air through the engine - but that can't be the whole story. I wonder if I ought to avoid the B gear altogether.. Things are going so well with the car I don't want to blow it by using that B gear too much.
     
  6. jerrymildred

    jerrymildred Senior Member

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    Yes, up to a point, and if there is room in the traction battery for more energy.


    The purpose of B mode is to use the engine as an air brake in order to avoid maxing out the battery charge and then risking overheated friction brakes. If it's a long hill that might overfill the battery, then use B. Otherwise, light braking should suffice. Cruise control will make is easier because the car will regenerate to keep from going faster than the set speed on downhill sections.

    As for the original question, hilly terrain often gives better mpg in a Prius depending on how you drive it. Driving our Prime around Colorado a couple years ago, we got 58-75 mpg actual at the pump. The indicated MPG is always a little optimistic on the Prius, but on the Gen2, due to that dumb gas tank bladder, you never know how full you got the tank, which makes it impossible to know if the miles/gallons arithmetic is right. You need to average several tanks to get a better picture.
     
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  7. DutchPrius

    DutchPrius Member

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    My guess is that the B-gear is for higher revs before shifting to then next gear and stays longer in a lower gear. I don't think you will blow up your engine that fast, but it's nog that good for you mpg average... I used it quite a lot when driving through the Alps during holidays, just to keep in the higher revs and not shifting too fast and (my guess) getting too much stress on the gearbox... I know from the old days that when driving with a caravan, you are not allowed to use overdrive to avoid damaging and overstressing the automatic gearbox. Things can get quite hot after a while...

    Best regards, Nick

    Black 2007 Prius
     
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  8. jerrymildred

    jerrymildred Senior Member

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    Ummmm... ya lost me. What are these gears you mention? The Prius uses an infinitely variable electronically controlled CVT. No belts, no gears. Just a continuum of voltage levels supplied to the two electric motor/generators. As the speed of MG2 varies, the speed of the car varies.

    Here's a good basics overview of the G2 transaxle, He also spends a few minutes explaining B mode.
     
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  9. oldtechaa

    oldtechaa Active Member

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    There are no gears to shift in a Prius. It's a single-speed planetary gear-set.

    B gear increases regeneration rate and pumps air through the engine.
     
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  10. John Dadmun

    John Dadmun Junior Member

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    All great information, thanks for sharing your knowledge Jerrymildred. I will adjust my driving accordingly!
     
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  11. DutchPrius

    DutchPrius Member

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    Oops, thanks for the info. Was pretty sure the Prius had "gears" like a conventional automatic gearbox. How come it feels like it shifts to a lower gear when accelerating hard? I was used to the kick down in my Mitsubishi, never realized this is completely different...

    But, back to the original topic and thanks for the lesson

    Best regards, Nick

    Black 2007 Prius
     
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  12. jerrymildred

    jerrymildred Senior Member

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    Because the engine speeds up like any engine. But there are no gears trading places or torque converters doing what they do. Just an adjustment to the voltage applied to the MGs which alters the RPM ration between the crankshaft and MG2, which is coupled to the front wheel. Watch the video again or, if you have time, check out one that goes into more detail.
     
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  13. fuzzy1

    fuzzy1 Senior Member

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    You can figure out the display accuracy by independently calculating MPG when filling up. As mentioned above, the Gen2 has a sometimes-inconsistent bladder, so keep a fuel log and figure averages over multiple tanks.

    Depending on the particular road slope and speed profile, and on the driver's style, mountain MPG can be anywhere from poor to excellent, even beating the best flat roads. My best mountain results appear with moderate shallow to moderate downhill grades that provide a good glide with little or no braking needed, allowing an efficient gravity recapture of the fuel energy burned on the climbing side. Think of it as a form of Pulse&Glide. Certain roads are far more amenable to such glides (safely) than others. But driver style is also important here, as it is very easy for an inefficient driver to squander and waste much of this glide energy.

    Descents needing significant braking won't do as well.

    The climbing side always takes more fuel, that is just an inherent fact of gravity. But the Prius engine is quite efficient over a fairly wide power range (more so on Gen3 and later, but Gen2 is still damn good), so I find the climbing details to be less important than the descending side. Less efficient drivers have less to mess up on the climbing side.
     
    #13 fuzzy1, Jun 5, 2021
    Last edited: Jun 5, 2021
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  14. John Dadmun

    John Dadmun Junior Member

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    I am taking your advice on this fuzzy1, thanks. I need also to keep an oil consumption log, have been trying to wing it but it is staying ahead of my guesses as to consumption. I have to start at the dot & then measure the oil going in & when or else I'll never get it just adding by eye so I have a 3 oz measuring cup in the car now. Trying to be mindful of using the B gear on descents when the battery is looking full. Using cruise a lot for hills since I figured out that I can quickly add or subtract 1mph by toggling the cruise lever up or down once, probably gonna wear it out :cautious:
     
  15. dbstoo

    dbstoo Active Member

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    I live in a valley. My commute used to include a one mile long 500 foot climb to a 800 ft above sea level, then 10 miles down to sea level. In my 2001 (gen 1) Prius I often made the round trip with better than 50 MPG. The downhill slope appeared to use virtually no energy other than gravity.
     
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  16. PriusCamper

    PriusCamper Senior Member

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    Best tip for high MPG hill climbing is keeping the RPM at 3500, which is where the engine has the most power... A week ago I climbed 130 miles of mountains from Sacramento Valley to over 5K feet in mountains of Southern Oregon and having a Bluetooth OBD2 reader connected to OBD Auto Doctor app on my phone made it really easy to hill climb by RPM... Best MPG I ever got climbing mountains!
     
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  17. ChapmanF

    ChapmanF Senior Member

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    I can't rule out possible changes to the 1NZ-FXE specs during the years of Gen 2, but at least the 2004 specs are max power from the engine of 76 HP at 5000 rpm. For Gen 1 it was 4500 rpm. Gen 3 (2ZR-FXE) has it a little higher, 5200 or 5300, I don't remember exactly. I don't think there's been a Prius engine that hits max power at 3500 rpm.
     
  18. fuzzy1

    fuzzy1 Senior Member

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    In my Gen3 experience, that sort of long shallow downslope, a 1.5% grade, is absolutely wonderful for recouping the energy of the initial climb, almost no matter how steep the climb was. But the reverse direction, with the steep 10% downslope, is MPG-unfriendly if the total elevation is enough to fill the battery with regeneration and still require considerable braking. If the start and end points had similar elevation, then I'd expect the shallow descent direction to produce significantly better MPG than the reverse steep descent direction. But the elevation difference between the two endpoints will ruin the comparison.

    It also doesn't help to mix in 3 different Prii generations, further complicating any comparisons.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    This chart doesn't include the Gen1, but clearly shows ever-increasing power at increasing RPM for the Gen2 and Gen3 engines:
    2010 Prius 2ZR-FXE engine efficiency map | PriusChat

    [​IMG]

    Perhaps he was thinking of near-maxium engine fuel efficiency, not maximum power. Though max efficiency for the overall system doesn't necessarily line up with the max efficiency for just the engine or other components.
     
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  20. ChapmanF

    ChapmanF Senior Member

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    I suspect that is what he meant and that makes good sense in context; I just didn't want to leave a post uncorrected saying max "power" at 3500, lest somebody else read it later and cite it somewhere else, and poof! a factoid is born.
     
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