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Air leaking from tire, valve stem noise

Discussion in 'Gen II Prius Technical Discussion' started by jaw444, Jan 15, 2009.

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  1. jaw444

    jaw444 Member

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    I got the Prius a week ago Friday.
    On Saturday, i got a new set of tires, Goodyear Triple Tread 195/60/15, at Discount Tire. I told them about the sensors. He said it was recommended to replace the grommets. The invoice said they replaced the valves. The installer said he put 37 psi in them.

    when i checked the tires later that night, some were lower than 37 and some were higher. maybe the guy was wrong.

    the next day, Sunday, i put air in the tires, 41 front 39 rear. The car had been driven less than a mile, to the gas station, after being in the garage all night.

    When i checked them later, (cold), some were lower than what i put in, not all of them were lower. i wish i'd written it all down but didn't realize yet that i would want to remember. Each tire was different, and they weren't balanced or even, front and rear.

    Every time i've checked the tires cold, when i touch the valve stem on the right front tire, a buzzing noise comes from inside the wheel, for about 2 seconds. I think it also happened when i checked the right rear tire once. The noise came from the front right, and always happens when i check the front right, but i think at least once it happened when i touched the right rear--but the noise didn't come from the rear, it came from the front.

    The right front tire is losing the most air. The left rear also loses air but not as much.

    The air was much lower on some of them on Tuesday (yesterday) so last night i went out and put 41/39 in them again. I only drove a few blocks to the dark deserted gas station.

    when i checked them this morning, they were all uneven again.

    Tonight i checked them, after the car had been sitting for hours. The right front tire was 33 after the night before i had put 41 in it. The left front tire was still 41. The left rear was 37, the right rear was still 39 like the night before.

    I'm wondering if any one has ever heard of a buzzing or humming noise caused by touching a valve stem when the car is cold. I took it to the Toyota agency today after work and asked about the leaking air and noise. The service manager did not see a nail and suggested i have Discount Tire check it. He dismissed the noise saying these cars make noises all the time. It didn't seem like he understood that this was always at the same time, when the car is cold.

    Could this have anything to do with the tire pressure sensors?

    I guess it could be a nail in the tire, but they're brand new and this problem started the day i got them, with very little driving on them, and the other tires have lost air as well. It's not just one.

    The TPMS light has not shown any problem. It comes on for a second and then goes off when i start the car.

    I plan to go to Discount Tire on Saturday, unless i can get off work early enough to do it tomorrow. I'm worried about having a problem that no one will be able to figure out.
  2. Rokeby

    Rokeby Member

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    Jaw444,

    There is in fact a valve in the "valve stem." To test for a leak through the
    stem, put a little spittle on the end of a finger and place it over the end of the
    stem. If there's a leak, there will be small bubbles. For a few bucks, you can
    buy a valve tool at most auto discount stores. Tighten the valves only finger
    tight so you don't strip the threads in the stem.

    To find a leak around the gasket in the rim, dilute some soap/detergent in a
    cup, and brush it around the gasket/grommet. Again, if there's a leak you'll
    see bubbles. In this case you should take the car back to whoever installed the
    new tires for repair... they screwed up.

    Hope this helps.
  3. hobbit

    hobbit Senior Member

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    I recently discovered that the Schrader valve cores in my stems
    were just a wee bit loose, and finally got to the point that
    a tire was starting to lose air. Very slowly, but the spit-test
    definitely showed an outgoing flow. Tightened 'em all up, which
    had never been checked/done since I got the stems, and no more
    trouble. I don't know if they were never tightened quite properly
    at the factory or the seating seals just squash down over time --
    maybe a combination of both factors, but if you've had a set of
    stems for more than, say, a year it's worth checking.
    .
    If your stems date from mid to late 2006 or beyond and *aren't*
    TPMS style, also check for cracking around the base...
    .
    _H*
  4. jaw444

    jaw444 Member

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    thanks for the replies.

    When you say to put spit on the end, do you mean the end where the cap goes, where i put the gauge when i check the pressure? Or the base where the valve attaches to the tire?

    the car is a 2007. The valve stems look like metal, shiny silver.

    The invoice from the tire change says that they replaced the stems.

    Someone on the PC forum told me that the sensors are attached to the valves and that the valves should not be replaced and don't need to be replaced, but this was after the tires had been installed so it was already done. I called Discount Tire to ask if they replaced the valves, what happened to the sensors. The man asked if i was sure i had sensors. It wasn't the same man i talked to when i took the car in. I said yes, i was hesitant because, i'm new to all this, i don't know anything about tires and didn't even know the prius had any sensors until the day i took the car in. But i said that the owners manual says there are sensors. He said the manuals talk about features that not all the cars have, it's an option. I said my car had all the options, package 6. So then he said that they don't take the whole valve out, they just replace the cores.

    Again, i don't know anything about these things. Are the sensors attached to the cores? What are the grommets? is that the same as the cores? The man i talked to the day i took the car in implied that the grommets would be replaced. I don't know what the grommet is. He said it was "recommended."

    Could any problem come up with the sensors, if the grommets or cores or valve stems are replaced?

    Could a problem with the sensor cause a buzzing noise when the stem is touched?

    Could a problem with a sensor cause leaking?

    While the sensor light does not indicate any problem, the tire pressure has gone much lower than the 37 pounds the installer said he put in. If the TPMS was working correctly, wouldn't i get an alert from the system warning light, when a tire goes down to 32 and 33 psi, which has happened since having those tires installed?

    Before i had the new tires put on, the car seemed to drive very nice, stable, level, well aligned, i appreciated this, but i only had it for one day at that point and drove it very little. After having the new tires put on, sometimes the car seems to 'rock' almost when going around a curve, i don't think it's as stable. I'm not sure, this is all new to me, i had three Honda Accords before i got he prius, so it's different from what i'm used to. Tires were always trouble free and a simple matter when putting new ones one.

    Any ideas what could cause a buzzing noise when touching the valve?
  5. qbee42

    qbee42 My other car is a boat

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    The valve stems contain the pressure monitor equipment. You do *not* replace the stems without spending big $$$.

    Valves (as compared to "valve stems") are inside the stems and can be replaced.

    If the tire shop replaced your stems, you will soon get a tire pressure warning light on the dash. It looks something like this: (!)

    The area to test with spit is where you put the pressure gauge, after unscrewing the cap (it's the hole on the end of the stem). The valves themselves are down inside the hole, and have that little pin sticking up from them (the pin that releases air when you press it). A car part store can help you with this, and sell you the little tool for tightening the valves.

    Tom
  6. jaw444

    jaw444 Member

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    tom, thanks for the clarification. The invoice says they replaced the "valve stems," that's what he wrote down. When i later called on the phone to ask about the sensors being in the stems, a guy who wasn't there when i came the day before said that it would've been the core they replaced, IF i did in fact have sensors, which he wasn't convinced of. By core, then, i guess that's what you refer to when you say there is a valve inside that can be replaced.

    I checked the pressure this morning, it wasn't down much, a pound or so, on all the tires. I checked the right front first. Every other time, i've checked it last. It did not make the buzzing noise. But when i got to the left rear, which was the third tire i checked, i heard the buzzing noise come from the front right.

    I will try to call Toyota today, the national office, and see if i can find a number to anyone that would know if such a buzzing during checking tire pressure is normal, or what it might mean. I hate to go back to Discount Tire without knowing what's going on. They probably have never heard the buzzing before and will just dismiss it as my imagination or a normal car sound--and maybe it is normal. But i haven't yet found another Prius owner who seems to have heard it before.
  7. JimN

    JimN Let the games begin!

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    TPMS is standard & listed on the window sticker. If a sensor is missing or damaged the warning light would be lit all the time. The warning light is activated when a tire loses 1/4 of the set pressure.
  8. jaw444

    jaw444 Member

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    That explains why the low pressure light doesn't come on. the tire installer put 37 psi in all tires. If he then reset the tpms, the light wouldn't come on until something like 27.5 --if i am understanding it right. I had previously heard that it comes on when the tires are 2 lbs under the set amount.

    I guess if i'm not getting a light saying there's a problem with the system, then it's OK.

    Maybe i'm just imagining the problem.

    I was using a tire pressure gauge that i got at the Toyota dealer the day after i got the car. It's a cheap digital one, and it was extremely hard for me to get it to fit the valve right so that air was always hissing out around it. Once in a while i'd get it right. I kept thinking i would get better at it, but it was always hard.

    Then i lost it, and i got a different kind, at OSH, it's a short little hose with the chuck on it and it has a round dial, and it was super easy to get it on the valve right. The same day, i also got another digital one, Accutire, and that one also easily fits right on the valve, no air comes hissing out. So, that was a couple of days ago, and i thought maybe my tires weren't really losing air, maybe it was just that i couldn't get meaningful readings from the other gauge. The air pressure seemed to be about what i had put into it a couple of nights before. But yesterday, the air was lower, with my new improved gauges. Today, the air in the front tires is lower than the back tires. I thought that i put 41 lbs in the front, on three different days. Today, it's 35 lbs in both front tires and 37 in the back. I had put 39 in the back.

    I was going to take the car back to Discount Tire, but then i got the new gauges and felt hopeful that there was really no problem, just the old gauge.

    Now i don't know. I feel like i don't know what i'm doing (obviously i don't).
  9. Rokeby

    Rokeby Member

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    jaw444,

    This tire pressure thing can make you crazy if you let it.

    First thing to do is to use just one gauge all the time. It sounds like the
    Accutire digital one that fits the valves without leaking is your best bet.

    Secondly, you need to take your readings for comparisons under near-
    identical conditions. It would be best to do this before the car has been
    driven, say in the morning, or later in the day after the car has been
    stationary or four or five hours.

    Air pressure in the tire can vary from what you put in due to:
    * Ambient outside air temperature. For every 10 degF change in outside
    temps, tire pressures change about 1 psi.
    * When you drive the car, the natural flexing of the side walls and other
    factors heats up the air in the tire and raises the pressure. So if you don't
    have an air pump, if you drive more than a mile to put in air, pressure
    readings are going to be high.

    So, lets say you checked your tires last week first thing in the morning and
    the outside temp was 60 degF, and you read 40/38 front/rear. No problem.

    If you retook the temps this morning with 50 degF outside temp, you'd
    expect to see 39/38. If you're a real stickler for precise tire pressures, you
    might then put 1 psi in each tire -- I don't think most folks would.

    Having to drive any distance to get air really boogers things up. Lets say
    your reading at your house are 37/36 psi, but you really want 41/39. Since
    you don't have a pump, you drive to a service station some distance away.

    When you get to the service station you retake the pressures and get 41/40.
    Don't panic. The extra pressure is from heating by the tire. (Because the
    front tires are more heavily loaded than the backs, they may heat up more
    than the backs.) What to do?

    Add the same number of PSI that the tires were off at your first reading at
    the house; 4 psi in the fronts, 3 psi in the backs to get 45/43 front/rear.
    Don't panic. The extra pressure is due to the heated air in the tires which is
    what happens everyday anyway, but you didn't know it because you weren't
    checking up on things. Just to be sure, you may want to recheck the tires
    the next morning when they are cold again.

    Of course life is not this simple. You may get different readings in the two
    front/rear tires. If so, it would be best to write things down as you go.

    Hope this helps.
  10. jaw444

    jaw444 Member

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    Thank you for the clarity about the ambiguity of tire pressure monitoring. :)

    I got an A/C 120v air pump, black and decker air station. I put air in the tires last night after the car had not been driven for about 4 hours. I changed them from 33/34 front, 36 rear to 41.5 front and 39.5 rear. The car's computer said that the temperature outside was in the low 60s. Today, around 2pm, I checked the pressure. The car had not been driven since the day before. The car's computer said the outside temperature was 68. The pressures were 40.5 front and 39/38.5 rear.

    does this sound normal or like something's wrong? They pretty much lost 1 lb each. The temperature change was probably abut 5 to 7 degrees higher today than last night. But it probably went lower during the night. It's definitely not warm or hot here at 2pm. It's mild but cool.

    The gauge I'm using seems very accurate. Anyway, virtually no air leaks out.

    Today, again, I tried the spit test, on the front tires only. I put spit on my finger and put it over the valve end, making a seal. I didn't see any bubbles, but am not sure i had enough spit? But after about 5 or 10 seconds of holding my finger on the left front tire valve, i heard a hissing sound coming from the valve under my finger which lasted a few seconds and then stopped. Then i took my finger off, and then coming from somewhere in the tire or wheel, i heard that buzzing noise that it often makes when i touch one of the stems, which lasted 2 or 3 seconds. At first that sound was coming only from the right front, but i've now heard it come from each tire. When it happens, only one tire does it, not all of them. It doesn't happen every time but fairly often. I must say it bothers me that no one seems to have heard of this or had it happen, that makes me think it's something abnormal. I tried the spit test on the other front tire, got no bubbles, and held it down for about 15 seconds or more, but didn't get that hissing sound.

    Still confused and concerned, hoping it's all just normal and OK. I still haven't tried putting soapy water on the tires. I'm scared to do any of this stuff, afraid i'll damage something. It weirded me out when the valve hissed when i had my finger/spit on it, like maybe i was making it worse. Whatever it is. But the change in the pressure was so minimal, i hope that was just because the tires got cooler.
  11. Rokeby

    Rokeby Member

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    jaw444,

    First off, I have never heard a "buzzing sound" when checking/inflating my
    tires. Which is not to say it's not happening, just I have never heard it. Since
    it happens when you are touching the stems, it is possible that it is air
    leaking around the base of the stem. Have you soaped that area yet? There
    is no way that putting a dilute detergent mixture on the stem bases and/or
    tires will hurt them. That's what happens every time you wash the car isn't it?

    As to the ~1 psi pressure discrepancies... Well, I don't see it as a big deal. A
    1 psi difference at 40 psi is ~2.5% which isn't even statistically significant.
    The gauge itself may be accurate to 2 psi or +/- 5%.

    Check and correct air pressure weekly. Believe me, that will be more often
    than 1 in 10,000 drivers in the general population, and probably 1 in 100
    here.

    Chill out brother. Driving your Prius is supposed to be fun... it shouldn't be
    driving you crazy.
  12. jaw444

    jaw444 Member

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    Thank you for all these replies and for your patience with my ignorance and confusion. This afternoon, i took the tire pressure (cold) and it was PERFECT. I am so happy about it. it was 41 front and 39 rear, which is pretty close to what i put in them with the new inflator two or three days ago. Thanks for explaining how it works, how it can go up and down, and the temperature and everything. This is the first time since i got the new tires that i've felt sure that the tires aren't leaking. Other than that worry, the car has been such fun. I'm glad i learned about tire pressure and ended up with a good gauge and compressor. Now i'll be sure to take good care of the tires, something i never did on any other car. thanks!!
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