I'm starting to suspect someone let the air out of my tire.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by dhanson865, Sep 23, 2014.

  1. dhanson865

    dhanson865 Expert and Devil's advocate

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    So I got a 70+ MPG run coming home last week and was feeling good. Got less MPG the next day, as I expected both legs of a commute can't be downhill. I noticed a continuing decline in MPG coming back again so I figured I'd let the car sit in the garage unused for a day or two on the weekend and check the tire pressure.

    Tire 1 was about 43 PSI
    Tire 2 was about 43 PSI
    Tire 3 was about 41 PSI
    Tire 4 was about 10 PSI

    OK, no big deal I must have picked up a nail or something. So I grab the air pump and pump it back to 25 PSI and let it sit overnight.

    Hmm, next morning I don't hear a leak, so it must be a slow leak, so I take it off the car, pump it up to 35 PSI and toss it in the front passenger floorboard of the car I'm driving to work. In full daylight the next day I check the tire for damage/punctures and don't see any nor do I hear a leak. Check the tire pressure and it is still around 35 PSI (actually read higher after sitting in the sun and warming up a little).

    OK so now I've pumped it back up to 42 and put it back on the car. I'll just drive on it tomorrow and check the tire pressure 3 times a day until I see a pattern of either no change or a pattern of loss.

    If it is losing air slowly I'm having a hard time wrapping my head around the 70+ MPG trip two days before I notice the 10 PSI tire.

    So assuming it doesn't lose pressure the logical explanation is that someone unscrewed my air valve cap, let the air out, put the cap back on and left. If so do I chalk it up to a one off or do I buy locking air valve caps?

    I'm still in the testing and diagnostics phase but I'm open to suggestions.
     
  2. JC91006

    JC91006 Senior Member

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    Bring it to a tire shop for proper diagnostic
     
  3. Fifine

    Fifine Member

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    ^ ^ ^

    what JC said. You haven't and probably do not possess the equipment to properly diagnose.

    OR - you may have bragged to the wrong person about getting 70 MPG!!!!!
    Quit it :p
     
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  4. dhanson865

    dhanson865 Expert and Devil's advocate

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    Proper equipment to properly diagnose a tire leak consists of a tub of water large enough to submerge the tire and enough light to see by.

    In this case I took it to the tire shop just in case it was something more complicated to fix (you know maybe they'd have to rebalance the tire after a plug/patch) and all they did after finding the leak is tighten the valve stem with a tool similar to one found on this page Amazon.com: valve stem tool

    So I drove 10 miles or so round trip for something I could have fixed myself with a cheap tool and a little bit of time and effort. No big deal but neither I nor the tire shop saw the need to use some expensive arcane equipment that you seem to imagine would be required here.

    Now I just have to go back behind them and put air in the tire since the tire shops idea of putting air in the tire is to inflate to 32 PSI.
     
  5. AzWxGuy

    AzWxGuy Weather Guy

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    I was going to suggest checking the valve core, but so many things can go wrong with a tire that it's always best to bring it to a professional. I consider it money well spent (if there was a charge) and priceless peace of mind at 75+mph.
     
  6. dhanson865

    dhanson865 Expert and Devil's advocate

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    oh and we now have a what but not a why.

    Did someone tamper with the valve stem or was it just not tightened enough to begin with when the tires were put on?

    If it was loose for an extended period it means I just didn't notice the gradual loss of air and I got 70+ MPG on a trip done with a tire below 20 PSI.

    If it was done as a quicker way to let air out of the tire then I have to wonder if it will happen again and if I need to buy locking valve covers.

    I'm leaning towards the accidental and away from the malicious at this point but it could be either.
     
  7. GrumpyCabbie

    GrumpyCabbie Senior Member

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    OR, how about the logical step being you picked up a nail, screw or thorn on your 70+mpg run? You'd be surprised how they can hide when you look for them on the outside, but they stand out a mile once the tyre is taken off.

    Just let your local friendly and trusted tyre shop take a look and fix the leak. That's the logical explanation ;)
     
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  8. The Electric Me

    The Electric Me Go Speed Go!

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    Just doesn't seem to make much sense as an act of vandalism.
    Of course vandalism really never makes any sense.

    The only scenario that seems to fit your results, would be if somebody decided they wanted to covertly let air out of your tire, with the sole intent of reducing your gas mileage.

    That's pretty specific "malice" and pretty careful execution.

    If you were magically missing your valve covers?
    Or if you came out to find your tire entirely flattened...Then I might believe it was malice and vandalism.

    But the idea of somebody carefully removing only "some" air, then carefully replacing the valve cover, with the intent of simply screwing with your gas mileage? Doesn't make much sense to me.

    My money is on the valve stem either never was right, or accidentally got damaged or loosened...it happens.

    I'd be paranoid enough to monitor for a while...and it's good to check tires monthly anyway....but I'd move on, assuming it was simply what it was.
     
  9. AzWxGuy

    AzWxGuy Weather Guy

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    I would be interested to know which side of the car wheel 4 is on. Sometimes these valve cores just spontaneously, or over time, loosen up. I think it might be some sort of torque hysteresis, which probably isn't the proper use of the word. You remember back in the day when they would put left-hand thread lug nuts on one side of the car. Same deal. But in that case, both rotations were in the same plane. These would be slightly out of alignment as the valve fitting is angled instead of parallel to the axis of rotation. It also might help that the TPMS valve body is rigid, where a flexible rubber body might absorb these transient forces. Or maybe I just think about this stuff way too much.
     
  10. dhanson865

    dhanson865 Expert and Devil's advocate

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    apparently you missed the post from the day before you replied saying I had already taken it to the tire shop and there was no nail, screw, or thorn.

    Heck it even seems you missed the earlier part of the same original post you quoted from a few days ago where I said I took the wheel off the car to thoroughly inspect the tire.

    This thread was well past the puncture possibility before you replied.
     
    #10 dhanson865, Sep 27, 2014
    Last edited: Sep 27, 2014
  11. dhanson865

    dhanson865 Expert and Devil's advocate

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    Interesting question so I'll give these answers.

    A. It was on the drivers side
    B. there is no TPMS on my car, it's a 2005.

    I think about stuff way too much also.
     
  12. dhanson865

    dhanson865 Expert and Devil's advocate

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    My thinking currently is that it isn't vandalism but as to the covertly part:

    I park in a large parking lot, the kind that would hold hundreds of cars but is wider than deep and runs along a large 4 story office building. My thought was that someone could have been letting the air out of the tire but while doing so someone else walked by. The person doing the wrong might have screwed the cap back on and walked away to avoid detection.

    I agree in hindsight this is a pretty low probability scenario. The fact that I still have the 4th cap instead of someone pocketing it or dropping it on the ground is the strongest clue that no one messed with it.

    I'd change the thread title but I don't have the ability. Maybe something like "surprise my tire lost 30 PSI and I still got good MPG?"
     
  13. GrumpyCabbie

    GrumpyCabbie Senior Member

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    I know. It's me letting your tyre down just to mess with your head.

    Me and a few guys on the forum were pissed that you were getting such great economy so take it in turns to pop over to your house to let one single tyre down.

    :p
     
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  14. exstudent

    exstudent Senior Member

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    Tire dunking at tire shop ruled out any nails/screws, or a hairline crack in the rim (happened to my buddy).

    I would be more inclined that someone is messing w/ you on purpose or its a complete stranger hitting Prius' specifically, or random cars (one of which was yours). If you are in a position of power (say any level of management), it could be a subordinate(s) who hate(s) you, and did this to be funny and add some misery to your life. Does the garage have a video camera? Ask for footage?
     
  15. wa-chiss

    wa-chiss Member

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    Did the tire place remove the tire off the rim or just place it in a tank of water? If they just placed it in a tank, it was off the car and unloaded. Nails can sink in below the outer edge of the tire making it hard to spot. Also, with the tire aired up to 42psi and unloaded, makes the rubber seal tighter against the nail. It's only until you flex the tire that you'd get a leak. I see this all the time in the shop.
     
  16. goldfinger

    goldfinger Active Member

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    You have an object in your tire, probable a nail. Most of the time its a very slow leak. Park just right, however, and you have a less slow leak. Just have your tire shop pull it off the rim and fix it.
     
  17. exstudent

    exstudent Senior Member

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    Ahh, that's why I recently was instructed by the mechanic, to turn the wheel all the way, so the tread was facing him. Then drive slowly in increments, upon command, while he sprayed a soapy water solution from a spray bottle, looking for bubbles. Eventually we found it. It was a small nail (looked like a finishing nail), buried in the tread, no visible sign of the head. Only the bubbles indicated its presence.
     
  18. GrumpyCabbie

    GrumpyCabbie Senior Member

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    You're wasting your time guys. The obvious answer is that someone must be sneaking over and letting the tyre down.

    Not a slow puncture, a nail, a screw, a thorn, a dodgy valve or a cracked or damaged alloy wheel, but some jealous hypermiler. It's the only logical explanation :ROFLMAO:
     
  19. dhanson865

    dhanson865 Expert and Devil's advocate

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    I assume they just dunked it, I know the entire tire was wet (not just the tread) and they mentioned the bubbles coming from the valve stem.

    I suppose it is possible that both I and they missed a very small puncture, I'll have to watch the PSI over the coming days and see if it loses any air.
     
  20. jdenenberg

    jdenenberg EE Professor

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    My Prius needs to have the rims cleaned with a wire brush and black goop put on them to ensure a good seal at the bead. These alloy wheels tend to corrode and cause slow leaks at the tire bead. Sometimes you can see the bubbles and sometimes you can't so I just clean and seal the bead as well as replace the valve stem to cure the problem.

    JeffD
     
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