Pulsing brakes at the bottom of a long steep hill

Discussion in 'Prius v Technical Discussion' started by MrZap, Feb 22, 2021.

  1. MrZap

    MrZap New Member

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    Update from today's drive up the hill, well actually down the hill. We went cross country skiing and headed down later than usual and so we were not dealing with other traffic that typically would have pushed us into a faster decent. B was used any time that we were heading down where the car needed to be slowed down. The battery was fully charged by about half way down and of course the revs went quite a bit higher after that point. In the past this would have made me concerned and I would have gone back to D, This time per advice above, I left it pumping air and the brakes only had to be used for the hills >8%. While slower, we were not overly slow coming down. The end result was no pulsing near the bottom.:)

    On what I believe is a totally unrelated note, when we stopped to fuel up this morning, I checked the engine oil level. I know I deserve a severe flaming for this but we had to add a full litre of oil, then another.....then a third and it was still just below the top mark. Ouch!:eek: I could try to make excuses (driven by two people, with regular changes we haven't had to add oil, just had the oil changed last month, etc, etc) but there really is none that is valid. I have no idea why I'm actually admitting to this and I'm tempted to stash this one under a carpet somewhere. :whistle: I have heard these engines will consume oil but this was a big surprise and no oil pressure warning light. Hopefully the engine is still in fair shape but that was really low. You know I will be checking religiously from now on.
     
  2. MrZap

    MrZap New Member

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    Wow. So now that I'm in the oil consumption club, I am seeing a lot of discussion on this topic. Is there any one post in particular that does a good job of laying out the approaches to mitigating the problem and some logic on choosing an approach? Looks like the real solution is new pistons and rings but that is not going to happen.
     
  3. fuzzy1

    fuzzy1 Senior Member

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    Good, I hope it keeps those pulses away every trip, not being a variable thing that still gets you some of the time.

    Note also that you don't need to let it slow you down below your preferred speed. Some users mistakenly believed that they needed to keep their foot off the gas pedal while using B mode. Nope. That gets maximum engine braking, but it is perfectly fine to push on the gas pedal to reduce engine braking and go faster. Modulate the degree of braking as you please, and seamlessly go into fuel-burning power production mode when reaching the bottom of a dip and starting to climb again, without needing to shift into D. When climbing or any other time that ICE power is needed, B behaves identical to D. (At least in most circumstances. There are some corner cases where it isn't identical, but not relevant to this ski road.)

    There is no real reason to take it out of B at all until past all the steep parts. For a hill like this, it doesn't do anything wrong on the flatter sections or even occasional uphills segments. It isn't like a traditional car where downshifts boost RPM all the time, B mode will do it only when needed for compression braking here, and act like regular D mode when B isn't needed. On this hill, at least.

    But do take it out of B when you get permanently down to the flats, short or shallow hills without a full battery, or slow or stop-and-go city traffic. Here, it will waste fuel by throwing away some of the energy that could be regenerated into the battery, and also prevent the ICE auto-shutoffs that otherwise would happen at stops, during glides and coast-downs, etc. Leaving it in B when not needed, won't hurt the car at all, it just disables some fuel saving functions and lightens your wallet a bit.
    That is good, it means you caught it earlier than the others who did have that light turn on. (The 'v' has a low pressure light just like the Liftback, I hope?) Hopefully that makes it less serious.

    Is the oil drain plug properly tightened? I had that on another vehicle a couple years ago, fortunately an oil slick betrayed it before the level dropped much.
    This road seems to have numerous good opportunities for this maneuver, something I also do, though infrequently.

    But I do it mostly on sparse rural roads. Numerous other ski access roads are not as favorable for this trick.
     
    #43 fuzzy1, Feb 26, 2021
    Last edited: Feb 26, 2021
    Mendel Leisk likes this.
  4. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    It’s somewhat a case of “couldn’t resist”, but still I DO think it’s a factor: a steady regiment of hill climbs and descents takes a toll on an engine; compared to flat land cruising, it ages an engine, fast.
     
  5. MrZap

    MrZap New Member

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    Thanks for all the great advice.
    I would agree that the steep hills are linked to the oil consumption but probably not the pulsing.

    Does this thread cover the reasonable steps to address the oil issue (along with the addition of an occ)? Is the occ a worthwhile addition or more like icing on the cake?
     
    #45 MrZap, Feb 26, 2021
    Last edited: Feb 26, 2021
  6. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    An effective and carefully installed Oil Catch Can is a good addition, but not going to reduce oil consumption to speak of. Besides avoiding hills, these may help:

    1. Keeping the oil changes to 6 months or 5000 miles, throughout the car’s life.

    2. Avoiding sustained high speed drives where practical

    3. Accelerating “conservatively”, staying at or below speed limits. This can be easier said in today’s Mad Max environment; just do what you can. Wearing a fedora might help?

    4. Avoiding short trips, do consolidate trips, etc

    5. Using block heater for a couple of hours before first cold start of the day, whenever practical

    6. Checking the dipstick frequently
     
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