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Prius B mode during engine break-in?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Entrevaux, Aug 17, 2016.

  1. Entrevaux

    Entrevaux New Member

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    Hello everybody,
    nice to meet you all.

    I am in process of breaking-in the engine of my new 2016 Prius (800 miles so far),
    accelerating smoothly and avoiding any excessive load.

    Going downhill yesterday, I applied B mode to do some "engine braking". The battery was fully charged at that moment.
    So, as the battery was fully charged, the electric motor revved up the ICE to its maximum, with that specific noise. I didn't expect that (though, I have read the explanation about B mode later on).

    Could you please tell me, can the usage of B mode in that way be harmful for the engine during break-in period?
    As it is better not to overrev the engine during break-in, and I didn't expect the car will do that for me :(


    P.S. Yes, I think I have some sort of BOS (Break-in obsession syndrome).

    Thank you in advance for your answers.
     
  2. alanclarkeau

    alanclarkeau Senior Member

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    I wouldn't be worrying - just drive it. The occasional spot of "variety" for the engine is likely to do it more good than harm.

    An engine like Prius, without a tachometer, and without a direct drive to the wheels, and running through the Hybrid Synergy drive system is likely to not be stressed anyway.
     
  3. Entrevaux

    Entrevaux New Member

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    Hello, alanclarkeau,

    thank you for your reply.

    Yes, I wouldn't have worried about it if it had happened during "normal" operation.

    My only concern is that engine is quite new, break-in is not yet completed, and revving it up to maximum, even without fuel injection, could probably make something bad with piston rings :(
    But maybe it is a myth, I am not sure.
     
  4. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    Toyota does a pretty good job at protecting its components. I would not be concerned.
     
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  5. bisco

    bisco cookie crumbler

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    congrats and welcome! agree with above, but wouldn't use it anymore until break in is finished. all the best!(y)
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    ^ Yes. The typical Prius owner, could go the life of the car without ever using B. It's only needed for extreme extended downhill grades, coming down mountains. The regen braking, where the car's electric motors act like generators, can only work so long. If the hybrid battery becomes fully charged, the car will revert to using the conventional brakes, and if they're worked long enough, they can overheat, become damaged and/or fail.

    But in normal, around town driving, you never need to use B.
     
  7. alanclarkeau

    alanclarkeau Senior Member

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    RELAX. Most engines these days are fairly well broken in before you get them. Remember the old days where you had specific RPM limits and extra oil changes - they've gone. (In contrast, race engines were loaded HARD from the start to ensure they broke in correctly.) From what I gather, the absolute worst thing you can do with a new engine is to keep it to the same speed without load for hours at a time, the occasional incursion into high load and high RPM won't damage it at all. I'm not sure of the "without fuel injection" aspect, but the oil pump is what lubricates the bores, not fuel.
     
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  8. Blizzard_Persona

    Blizzard_Persona Senior Member

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    It's a CVT transmission with synergy drive!

    That equates to a varing rpm at all times, which is exactly how an engine is supposed to be broken in.

    Drive it as normal.


    P.s. The old rule to never use cruise control while breaking in an engine for extended periods (i.e. Don't take a road trip across the country with cc set the entire way) might still hold true, but yet again think about it.... With radar cruise or not the engine rpms are constantly varing with every up/downhill.


    Again, just drive it...


    I've broken in motorcycles and cars both the easy way and the hard (moto tune way) and maybe except for high performance high compression turbo cars it didn't seem to make a bit of difference.
     
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  9. MrMischief

    MrMischief Active Member

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    The owners manual says to vary the engine speed during break in (I forget how many miles now off the top of my head). Sounds like you're doing just that.

    BTW if it is bad for it, I'm right there with you. I think I had 500 miles on it when I first came down one of the steepest (if not THE steepest) sections of interstate in the US. I used B the entire way down, ICE screaming bloody murder while the car continued to pick up speed. I started at 55 mph and over 80 mph by the bottom.
     
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  10. CR94

    CR94 Senior Member

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    How did you determine it was "revving up to maximum"? The computers won't let you overspeed the engine, so don't worry too much about it.

    Agree with others that "B" should be used only descending mountains or hills high enough and steep enough to require prolonged braking.
     
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  11. Entrevaux

    Entrevaux New Member

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    Well, I didn't have an OBD2 scanner connected, but judging from the noise it was around 5 000 RPM, the "maximum" for Prius engines.
    So, the problem for me is not the high RPM itself when using B mode, but high RPM during break-in.

    But (maybe I am becoming paranoid about it) I have noticed that the engine began to start more smoothly... for a couple of hours.



    Yes, I agree, too. That was exactly the case, but I didn't expect that usage of B mode will result in that kind of engine screaming :\

     
    #11 Entrevaux, Aug 19, 2016
    Last edited: Aug 19, 2016
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  12. Entrevaux

    Entrevaux New Member

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    Thank you for your answer,
    by the way, I also concerned about the noise itself. The noise was really like a scream, not very clear and stable (like it can be), but with some extraneous noises which may seem like the ones produced by turbo engine.
     
  13. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    If he lives in the Pyrenees or the Alps, he might be 9000 foot elevation, so B could be important. Else where in France, not so much.
     
  14. MrMischief

    MrMischief Active Member

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    My understanding is that it sounds goofy because it's only pumping air, no explosions. But I agree it sounds strange. When I first heard it I was wondering where the Honda with the huge exhaust tip was.

    In my experience, B mode is pretty much useless on mountain passes. There is not enough engine braking to control your speed. I don't know how Toyota could have done a better job, but they should improve it.

    My two thoughts..... They could use rheostatic braking with a computer controller switch. When in B mode and the battery is full, send generated current to a resistor bank that burns off excess electric. I think I'd prefer this mounted on the back of the car so when they're in use you get a bank of red hot resistors shining out the back, like jet engines! (I'm like, 8 years old.....) Other than where to place the toasters, I don't see that this adds much complication to the current system. OR they could use eddy current braking. Downside is that would take power from your traction battery sort of defeating the regenerative braking but I'm sure someone smarter than me can figure out a way to have both. It would probably add quite a bit of complexity.
     
  15. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Are you expecting it to work without you pressing the brakes? Because when you do brake in B the engine pumps a LOT of air to slow you down. (Perhaps the most non intuitive part of a Prius, the harder you brake in B, the louder it gets)
     
  16. CR94

    CR94 Senior Member

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    Really? To me, that feature seems a perfectly logical and reasonable behavior. Stepping on the brake pedal tells the computers you want more retardation. The only way to provide that without needlessly heating the mechanical brakes or overcharging the battery (or adding the complication and weight of resistors) is to spin the engine faster.
     
  17. alanclarkeau

    alanclarkeau Senior Member

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    Maybe it could be connected to a FLUX CAPACITOR ...
     
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  18. MrMischief

    MrMischief Active Member

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    hmmm.... Yes. Yes I am expecting it to work without pressing the brake because that is what every other car does and it seems to be what the Prius does. Coming down I-70 from Eisenhower Tunnel to Silverthorne the ICE is screaming, without me being on the brake, and the car continues to pick up a LOT of speed. Maybe it's fine for the Blue Ridge Parkway, but B mode is pretty close to useless in the Rockies.
     
  19. wrprice

    wrprice Active Member

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    I took I-25 out of Denver and used B-mode on appropriate stretches between there and New Mexico. I thought it did a reasonable job. Sure, the speed would creep up slowly when coasting, but I found that extra braking was only necessary occasionally. I think those were mostly, what, 6% grades? Steeper than that and, yeah, you'll be using the brake pedal.
     
  20. axle2152

    axle2152 Active Member

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    Unfortunately where I live I had to use B on the way home from the dealer after buying it... I live about 100 west of Asheville and some fairly steep grades 6-9%, I probably could have kept hitting the brakes but didn't want to get brand new brake shoes and rotors too hot either.
     
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