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Battery voltage dropping after new alt, battery and serpentine belt

Discussion in '5th Gen 4Runners (2010-2024)' started by almostbasic, Jul 9, 2023.

  1. Jul 9, 2023 at 7:30 AM
    #1
    almostbasic

    almostbasic [OP] New Member

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    The alternator and battery were dying on my 2011 4runner Trail, so replaced them along with a new serpentine belt. I used an Ultima alternator from O’Reilly.

    It started right up with no issues. My aftermarket stereo shows vehicle info, including battery voltage, which stayed between 13.1 and 13.3 for several hours of driving.

    It started raining VERY HARD and after a while, the voltage would slip down to 12.0 - 12.5 and the dashboard battery light would come on. Within a few seconds it would go back up to the low 13’s.

    It seemed to happen most under hard acceleration and on the highway, but was not exclusive to those situations.

    As I was finishing up on my truck, it started raining, and it was outside, so I didn’t put any dielectric grease on the battery terminals. I did spray them with electronics cleaner but only let it sit for a few seconds and wiped it off with a shop towel, but they weren’t very dirty and weren’t corroded at all.

    There was no belt whine at all the whole time I was driving.

    What could cause the voltage to slip down randomly for a few seconds before going back up? It never lasted more than a few seconds, but it’s still concerning to say the least.

    Thanks in advance!
     
  2. Jul 9, 2023 at 8:04 AM
    #2
    TrueTexas

    TrueTexas New Member

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    Sounds like the alternator you bought is no good. Should be pushing 14.1 - 14.5.

    I'm guessing our alternators have an internal voltage regulator as most modern ones do.
     
  3. Jul 9, 2023 at 8:12 AM
    #3
    almostbasic

    almostbasic [OP] New Member

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    Thank you for the reply. I really hope it’s not that, it was a pain installing it. The voltage never went over 13.7, but mostly sat around 13.2v.

    Do you think a bad alt would cause it to randomly drop down for 3 - 10 seconds, then jump right back up? I was under the impression that a failing alternator would cause the voltage to steadily and slowly drop down, but I could definitely be mistaken.

    The fact that it only seemed to happen when it rained seemed odd as well.

    Someone told me the belt might need to be tightened, and that it may have been slipping, thus causing the alt to not charge temporarily. It mostly happened under hard acceleration and on the highway and while raining, all of which seems like things that could make the belt more likely to slip, but I really don’t know. I have very limited experience with this stuff.

    If the belt was slipping a little the whole time, would that cause the voltage to stick around 13.2?
     
  4. Jul 9, 2023 at 8:36 AM
    #4
    TrueTexas

    TrueTexas New Member

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    If the belt were slipping, it may cause the voltage to be all over the place. Probably not drop over time. Sounds like that may be a heat related issue with the voltage regulator or a winding / brushes issue. I don't think you can tighten the belt. Doesn't it have a tensioner that you needed to turn with a breaker to get the belt off/on?

    A bad alternative or voltage reg would cause fluctuations. It should be a relatively constant 14.1-14.5.

    Check the routing of the belt. Is it correct?

    Parts store parts are notoriously poor quality. Napa is the exception in many cases. But can't beat quality of toyota / denso etc... not sure who makes the 4Runner OEM alternator. May want to check Rock Auto for a better part.

    I know it's a pain but you've done it once, should be faster this time
     
    almostbasic[OP] likes this.
  5. Jul 9, 2023 at 9:45 AM
    #5
    RumHamRunner73

    RumHamRunner73 Dead on with a zero

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    I think the OEM is by Denso, Not 100%.

    With that being said, i have gotten and installed re manufactured alternators and starters that failed very quickly after installing. This has always made me concerned of the "rebuild and testing steps" taken during the process.

    Makes a strong case in sometimes staying with OEM if the budget doesn't take a beating.
     
    almostbasic[OP] likes this.
  6. Jul 9, 2023 at 10:02 AM
    #6
    JETSPD1477

    JETSPD1477 New

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    more often than not you’d hear a slipping belt esp under load.
     
    almostbasic[OP] likes this.
  7. Jul 9, 2023 at 10:18 AM
    #7
    steelevo

    steelevo Not so new anymore...

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    I would get an actual test done by a mechanic on the battery and alternator condition and not rely on what an aftermarket stereo is measuring.
     
  8. Jul 9, 2023 at 10:32 AM
    #8
    TrueTexas

    TrueTexas New Member

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    This is a fair point!!!
     
    almostbasic[OP] likes this.
  9. Jul 9, 2023 at 12:37 PM
    #9
    almostbasic

    almostbasic [OP] New Member

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    The only reason I think it’s accurate, is because the dashboard battery light also came on.
     
  10. Jul 9, 2023 at 12:53 PM
    #10
    AuSeeker

    AuSeeker Old As Dirt

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    Go back to O'Reilly and have them test the alternator and battery you bought from them, don' tell them you bought them there until after they test them!!!

    It sounds like the voltage regulator inside the alternator is bad.

    Just an FYI most all auto parts stores will test your alternator, battery, and check for codes etc. free of charge!!
     
    almostbasic[OP] likes this.
  11. Jul 9, 2023 at 1:23 PM
    #11
    almostbasic

    almostbasic [OP] New Member

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    The plot thickens…
    The black plastic cover that goes over a bolt on the alternator appears to be melted. Any thoughts on what might cause this?

    Used my voltmeter and got:
    12.5v with car off
    Turned it on and read 13.7
    Turned on headlights and AC and it dropped to 12.5v and did not go back up.
    Turned off headlights and AC and it stayed at 12.5v

    325471F4-CB6F-4758-B2F6-F22CC9A17C3E.jpg
     
  12. Jul 9, 2023 at 2:05 PM
    #12
    AuSeeker

    AuSeeker Old As Dirt

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    Again sounds like a malfunctioning voltage regulator.
     
  13. Jul 9, 2023 at 4:58 PM
    #13
    rmiked

    rmiked New Member

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    I have a 2023 ORP. I hooked up voltmeter to the battery terminals and ran a few tests. Vehicle off (for hours) the voltage is reading around 12.75 volts. When started (A/C off, no lights , no rear window defroster) it immediately went to 13.95-14.10 volts. I turned on the rear window defroster (along with side view mirrors) and the voltage momentarily drops to 13.85 then back to 14.10. I progressively turned on lights (low beam), then fog lights, then bright lights, then A/C. In each case there is a momentary drop of a couple tenths of volt. Then back to 14 -14.1 volts. I think there is a load detection circuit and the voltage regulator is managing the current output of alternator to keep the voltage near 14.0 volts regardless of load. If the running voltage is much lower than 13.8 volts that sounds low based on what I just measured. My battery is relatively new in that my 4 Runner only has 1600 miles on it. Perhaps an older battery is more difficult maintain voltage?
     
  14. Jul 9, 2023 at 5:26 PM
    #14
    Too Stroked

    Too Stroked New Member

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    O'Reilly electrical parts are noted for poor quality. I can't tell you how many of their alternators are bad right out of the box. I'd have it tested, but if it's bad - and I think it is - I'd put an OEM / Denso alternator in. The only parts store electrical parts I even come close to trusting are NAPA.
     
    Rocko9999 and almostbasic[OP] like this.
  15. Jul 9, 2023 at 5:58 PM
    #15
    Glenn Goodlett

    Glenn Goodlett New Member

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    If I'm not mistaken the belt has a tensioner so there is no tightening the belt. It's done automatically. A loose or bad electrical connection can make strange things happen, so it might be worthwhile checking the connections. Other than that, it's probably the alternator. Could be a sticky brush in the alternator. I could not really get a view of the melted plastic so I'm not sure what to say about that.
     
  16. Jul 10, 2023 at 2:09 AM
    #16
    TrailGuy2016

    TrailGuy2016 New Member

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    I'm betting on the O'Reilly alternator being crappy.
     
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  17. Jul 10, 2023 at 7:21 AM
    #17
    almostbasic

    almostbasic [OP] New Member

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    It was the connection to the alt under that black plastic cover that melted. The nut apparently broke when I tightened it before and I didn’t notice, so it had a bad connection and must have been arcing, thus melting the plastic cover.

    I cleaned everything up with electronic cleaner and put on a different nut. I cleaned up the battery cables for good measure.

    New readings:

    Battery with truck off: 12.5v
    Battery with truck on: 14.1v
    Battery with truck and all accessories on: 14.1v
    My face: smiling

    Thank you so much for the help, I am so happy I didn’t have to pull the alternator. That’s really not a fun job
     
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  18. Jul 10, 2023 at 7:41 AM
    #18
    almostbasic

    almostbasic [OP] New Member

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    How important is that black cover? Do I need to get a new one? Is it safe to drive without it?

    I was thinking of just hitting it with some dielectric grease to insulate it.
     
  19. Jul 10, 2023 at 7:52 AM
    #19
    Glenn Goodlett

    Glenn Goodlett New Member

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    I don't think it would hurt to not have the cover. Just be mindful when working in that area as to not let a wrench or screwdriver short out.
     
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  20. Jul 10, 2023 at 12:36 PM
    #20
    08TXRunner

    08TXRunner New Member

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    OP, you're darn lucky that didn't dead short on you. That would have been a mess.
     
  21. Jul 10, 2023 at 12:47 PM
    #21
    Dillusion

    Dillusion Resident A**h***

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    O riley is the first problem.

    I'd honestly ask for money back instead of a replacement and go to Napa if not getting OEM.
     
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  22. Jul 10, 2023 at 6:06 PM
    #22
    Too Stroked

    Too Stroked New Member

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    Glad to hear you tracked down the problem. One caution though. A loose connection will cause arcing. Arcing will remove the plating from electrical connections. No plating = no corrosion resistance. This will lead to problems down the road.
     

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