Engine revving high. Help

Discussion in 'Prius c Main Forum' started by Josh331, Jun 20, 2021.

  1. Josh331

    Josh331 Junior Member

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    I drive my 2012 C for a living and I’ve noticed lately my engine revving high after I take my foot off the gas. Doesn’t do it for very long, maybe just a few seconds or more, but I noticed it doing it the most when it’s really hot outside. First thing in the morning it’s perfect, doesn’t do it at all, but where I am at, it’s in the mid-80s so that sucker revs.
    I’m going on a little road trip tomorrow, about 1200 miles and I’m just making sure the car is alright to drive. car itself has 275,000 miles but the engine and hybrid battery have around 140k. I read on a post about my same issue that it’s just the engine protecting the battery and that it’s not bad well, It never did it all the time in years past so I’m just concerned. Thanks for the help.
     
  2. bisco

    bisco cookie crumbler

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    could be the engine protecting a hot battery. is the battery icon fluctuating at all?
     
  3. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Yeah sounds like the computer is trying to dump some heat out of the battery. One of the fastest ways to do this is to use battery power to spin the gas engine. It isn't burning any fuel, it's just make-work; trying to discharge the battery a bit to cool it down.

    Discharging a nickel metal hydride battery will absorb some heat, which might seem counterintuitive but there's your weird science for the day.

    Keep your battery fan clean and free of obstructions and use plenty of air conditioning. The battery breathes cabin air.

    Good luck!
     
  4. Josh331

    Josh331 Junior Member

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    Yes the battery icon is constantly fluctuating
     
  5. bisco

    bisco cookie crumbler

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    yeah, that's a bad hybrid battery :unsure:
     
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Agreed, if it is having thermal problems AND you're starting to see a warning light then that battery pack is already in trouble.

    I'd expect a 2012 to need a new one approximately now anyhow.
     
  7. ChapmanF

    ChapmanF Senior Member

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    I've seen this before, but I don't know enough about this endothermic effect to know how to compare it to the I²R heating effect.

    I know more about how to estimate the heating effect: I'm used to seeing Dr. Prius-style apps reporting internal resistance somewhere around 21 mΩ per block, or .21 Ω for a ten-block Prius c battery. A twenty-amp discharge would be making 20²(.21) = 84 watts of heat or so. I wonder how large the endothermic effect is in comparison, and which effect dominates in practice?

    I did find this in a quick search:

    If that's so, then I'd expect that effect to end up kind of small, and the I²R heating to still be the dominant effect.
     
  8. Josh331

    Josh331 Junior Member

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    I don’t have a warning light, the battery just drops down to two bars (then the gas engine stays on longer) then a little bit later I have almost full bars then it drops down to two bars again. Does it all day long, probably a lot more now that it’s hot.

    that battery has around 150k miles on it. Still think I have a bad battery? Or is it simply just the engine protecting it? - my only thing If that is true, is it never used to do it all the time like this. But the parts are used so maybe this is all normal.
     
  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Ignore odometer, read calendar.

    Toyota put an 8 year warranty on that battery. A lot of their profit margin depends on what happens in years 8-9, if you catch my drift.

    Put a new battery in that car and it will be an all-you-can-eat buffet for another 8-10 years, or plan to bail out soon.

    And again, get in there and clean the battery cooling system with a vacuum. There are youtube how-tos.
     
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  10. ChapmanF

    ChapmanF Senior Member

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    Methinks that could sound more cliff-like than what really happens. If I remember right the first stats published by Consumer Reports on the earliest Prii (which they couldn't publish until year twelve because they flat out didn't have enough battery failure data before then), they were seeing about 4% replaced by year 11, 5% by year 12.

    My Gen 1 was in year 15 when I sold it. I heard the buyer did change the traction battery shortly after, but the buyer ran a hybrid shop and might have done that anyway. It had never given me a code, but I had caught the system running some strange equalizing cycles on it in the last few years. Car was performing fine.

    My current Gen 3 is in year 11 and doing great.

    We know the cars may have some tricks up their sleeves, like those equalize cycles in my Gen 1, they might start using more as the battery ages. I haven't noticed my Gen 3 doing anything like that yet, but possibly it knows similar tricks. If that's what's happening, it's clearly programmed in to get you the maximum useful battery life. So one attitude you could choose to take would be to just relax until it actually codes for a battery problem, and spend the money then. It could be soon or it could still be a few years down the road.
     
  11. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I'm in strong personal support of that- but OP said he was driving it for a living.

    I tend to keep my working tools in better shape than my fishing tools, eh?

    Also the c model has a smaller battery- your cars would have had a longer warranty for their batteries, and everything I've read suggests that the larger packs in the big Prius last longer.

    re: the battery heat vs. chemistry: My own experience with small, hobby grade nimh batteries agrees that there isn't a major cooling effect, and if the discharge is continued there will be a heating effect later in the run.

    I don't know if Toyota is trying to overtly cool the battery, or if they're specifically trying to lower the state-of-charge while above a certain temp. But I've seen enough reports of the behavior to be convinced that this is a programmed defense feature taken when the battery is hot and full, and it seems to happen much more frequently with age.
     
  12. Josh331

    Josh331 Junior Member

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    Just cleaned out that battery vent. Keep in mind I’m on the middle of my trip, did it in port Angeles an hour following the 101 all the way down to Seaside and then back home to Coeur d’Alene Idaho. That vent had never been cleaned since that hybrid battery got put back there a couple years ago. You can imagine what it look like, so I vacuumed it all out good
     
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