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Oh My! using 'B' or braking a lot will crush your mileage

Discussion in 'Gen 3 Prius Fuel Economy' started by Supertone07, Aug 29, 2016.

  1. Supertone07

    Supertone07 New Member

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    Just tried two tanks of petrol without using 'B' or 'braking' on the shift lever and suddenly my mileage was back to "normal". I was using 'B' to help slow down almost all the time as to help not burn up the brakes and simply because its easier to use than the brake pedal. ;-). I had been do this since last winter and thought my mileage decrease was do to cold weather, which it probably was, or at least in part. I was struggling to get 47 MPG over all when I had been in the mid 50's. So, I tried the whole slue of remedies mentioned here, like fuel injector cleaners, tire pressure and 12V battery capacity all of which made marginal improvements. It wasn't until I read a post, forgot who's now, but it said to leave the shift lever in 'D' always when driving. So I thought I'd give it a go and sure enough my last two tanks gave up 53 and 56 MPG! Just thought I would pass it along in case some others are doing the same thing. Love this forum!
     
  2. The Electric Me

    The Electric Me Go Speed Go!

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    Almost any way I present this sounds "snarky" and sarcastic.
    But I wish people would use "B" as Toyota presents the usage.
    Which is to shift into B on longer downhill descents.
    And that is about it.

    The Prius is NOT a manual transmission vehicle. B is NOT downshifting.
    Just use the system as designed.
    Any brake "savings" constantly shifting into "B" to slow down "might" and only might create is off-set against the misuse of the E-CVT transmission and the bypassing of how the brakes and HSD are suppose to work. You're suppose to use that "Brake Pedal" for braking. I don't buy the contention that using the selector knob to pick "B" is easier than just pressing the brake pedal.

    You just discovered...driving your Prius as designed...is better than applying your speculation as to how something should be used.
     
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  3. wjtracy

    wjtracy Senior Member

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    Oh man, we have to put "B mode overuse" on our low MPG list.
    The thing is your hybrid car never uses the brakes much except maybe in B mode...normally the elec motor is spinning in reverse to slow down the vehicle - so you do not need B. If you are going down a big mountain like Rt. 40 in Uniontown PA, and your battery gets totally charged up, then the elec motor no longer has a place to store the electrons during braking, that's when B mode helps you reduce use of brake pads.
     
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  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    B is designed to waste energy. (and wasting energy reduces MPG)

    If you are descending a long steep hill (over 600 foot vertical) your HV battery may heat up from over charging and refuse to charge more, leaving you with the friction brakes. By adding B at the top of long downhills, you waste some energy as an air pump (the harder you brake, the louder you get, this was counter intuitive to me) so the HV battery does not heat up as fast and you go farther down the hill before it fills up.

    Other than that, there is almost no point to ever using B. (Some owners use it between 24 and 7 MPH, but I do not drive that slow)
     
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  5. john1701a

    john1701a Prius Guru

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    I've found it handy for slowing in certain slippery winter driving.
     
  6. bisco

    bisco cookie crumbler

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    don't use B! isco.
     
  7. Maarten28

    Maarten28 Active Member

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    Maybe you need to do more with the braking pedal than just slamming it.

    To the OP: you also never noticed that the cruisecontrol does not work in B-mode?
     
  8. CR94

    CR94 Senior Member

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    I agree, mostly. "B" may also be worth using in hot weather to minimize further heating the battery on more moderate hills that require stopping at the bottom. I do that if BT2 is near or over about 110°F. Conserving fuel is fine, but saving the battery is even better.
     
  9. cproaudio

    cproaudio Speedlock Overrider

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    You know the engine doesn't shut off in B mode when you come to a complete stop right? That's where your poor gas mileage comes from. Also in B mode, the ICE is robbing your Regen so you don't recover nearly as much energy as if your were to leave it in D. The only time I use B mode while not going downhill is when the weather gets too hot and the Regen stops working. B mode forces the Regen to recover some energy that would otherwise lost to mechanical braking.
     
  10. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Let me translate: I use B mode when it gets so hot my car tries to protect the battery from further internal heating and I want to heat it to dangerous levels anyways. I over ride the safety of the battery for my own goals.
     
  11. cproaudio

    cproaudio Speedlock Overrider

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    Yeah that sounds about right. B mode forces about 15-20 amps of Regen where as without only allows the minimum Regen which is about 10-15 amps.
     
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    I was not aware of that, handy during coolant change, or whenever you WANT engine to run?
     
  13. john1701a

    john1701a Prius Guru

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    That's quite insulting, especially to someone who's driven on snow & ice for 30 years.

    I started with non-powered brakes you had to pump, then got powered drums, then discs, then anti-lock. Now having the added benefit of gradual slowing without even needing to push the pedal is a nice perk.
     
  14. trip1027

    trip1027 Member

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    I use Brown mode alot, when coming off of the interstate, long downhills, but I only put it on when slowing I also use neutral on long downhills when no one is around to see if I can get to the next uphill while my engine is off. The longest I have gone in N while only useing brakes is 16 miles... I was proud couldn't do it again because of traffic though

    SM-N920V ?
     
  15. trip1027

    trip1027 Member

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    Hey bisco u ever use this stuff before? 1473120979838.jpeg

    SM-N920V ?
     
  16. fuzzy1

    fuzzy1 Senior Member

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    It is one of the questions on the standard questionnaire:
    '- Are you driving using D or B mode?'

    Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat
    Hardly. 'B' mode won't provide much more braking force than normal regenerative braking with the foot pedal (provided the battery is not filled), while still saving the brake pads.