Very slow air leak in tire

[Bob Johnson]

Please read the whole message before responding. Several weeks ago one of the tires on my Sedan was very low in air pressure. I pumped it up and the next day it was low again. I took out the tube and tested it for leaks. I could not find any. So I put in a new tube. I was checking it every time I drove the car. Today I was going to drive it and the tire was low (not flat but low about 10lbs). I exchanged the wheel/tire for the spare. I set the wheel/tire aside and inflated it to 40 lbs. A few hours later the pressure was down to 30 lbs. I took out the new tube and tested it for leaks by inflating it with enough pressure to make the tube almost twice it's normal diameter. I put it in water and did not see any air bubbles, including at the valve. I put the tube back in and inflated it up to 40 lbs. I checked the valve with soapy water and no bubbles. Initially there were bubbles coming out at the hole in the rim for the valve stem. I thought this might be air that was trapped between the outside of the tube and the inside of the tire. It has been about 1/2 hour since I inflated the tire and there are still bubbles coming out of the hole when I spray on soapy water. The bubbles appear at a rate of about 1 every 3 seconds. The wheel does have a rim liner and I ran my hand over the entire surface where the tube touches the rim and did not feel any sharp areas. The inside of the tire was made with lots of ribs so it was hard to feel for any problems. I have checked the valve stems on both tubes and I could not find any cuts or holes.


Now I have 2 tubes which test OK when out of the tire. And a tire/rim combination that appears to be creating slow leaks in the tubes.


HELP
Bob

[Randy in ca]

Could it be that the pressure in the tube, when it's out of the tire, is just so much lower than the 40 psi it's at when the tire is inflated? Any idea what pressure is in the tube when inflated outside of the tire? Still pretty low I would guess. Does the tire ever go completely flat if left? Kind of searching here, but all that seems to make sense is that it only leaks at fairly high pressures (?). Strange that 2 different tubes would do the same though. Kinda strange. Good luck.

[Harpkatt]

Tubes in cars are the same as tubes in a bicycle, albeit typically thicker. There's nothing special here though. One thing you should know is that Co2,is actually soluble in butyl rubber. This means that even if a tire is good and defect free air can escape directly through the rubber as it actually becomes a solution with the rubber. Thinner inner tubes will for this reason leak faster. Still deflating in one day would lead me to believe its not this.

Usually placing the tube in a large container of water does help find the leak. I would suggest checking again. After you find a hole lining the inner tubes leak up with the tire helps show where something may be poking through the tire into the tube. You've done everything the right way, so I would check again. Additionally look for any signs of the inner tube chaffing against the rubber or rim. Sometimes the inner tube can become pinched between the rim and tire when first installing and this can cause a leak. As an attempt to prevent this fill the tube just until it starts to take shape before installing in the tire.

Check near the valve on both tubes, a sharp rim can easily slice a valve stem, unless of course its a metal stem.

Good luck, you'll find it

[Bob Johnson]

When inflating the tube I put int about 6 lbs of pressure then deflated the tube so it would was even in the tire.

[ronn]

I have had the same problem and 2/3 of the time, there is a leak, crack around the valve stem. flex it a bit after pumping the tube up.

[Dodge]

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Hi Bob,
Did you figure it out? I saw you driving around Novato.

Dodge

[nkaminar]

in 1966 on a trip to San Diego from San Luis Obispo I got 7 flat tires. I kept patching the tube but it kept getting flat. I finally found the nail that was poking through the tire.

The air coming though the valve stem opening indicates a leak in the tube. Check again for a something poking through the tire or a sharp somewhere.

[Dennisfly]

Have you tried using a soapy solution to check the tubes?

[Bob Johnson]

I checked the tire this morning and it is holding air at 40 lbs. The bubbles at the hole for the valve stem have stopped. Is it magic or are the Model A gods just messing with me?


Yes I have checked the tubes. No leaks when out of the tire. No cracks at valve stems. It is hard to check the inside of the tire because it was manufactured with ribs on the inside surface.


Very strange because first tube held air for over a year and over 1000 miles. The second one lasted weeks and over 100 miles. At this point I can not trust either tube or the wheel/tire.

[Redbird]

Did you looks over the thread with a fine tooth comb to make sure no nails,etc?

[Gary Karr]

Bob, do you have rubber stems or metal valve stems? Sometimes taking the valve core out and inspecting it and reinstalling it will do the trick. The new short valve cores are Chinese made and sometimes not as good as older US made cores.

[noboD]

It didn't fix itself. When in the tire you have 40 PSI. When out you have about 2. use soapy water and patience, the leak is still there.

[Brad in Germany]

With the tube out of the tire, try dragging a pair of sheer pantyhose around in the tire to see if anything catches on it. You can do the same around the rim as well. Works great for finding those very small protrusions through the tire, as well as finding any rust or paint chips flaking off around the rim which might compromise the inner tube.

I had a similar problem and it turned out that the base of the rubber valve stem was dry rotted and cracked. It only leaked under 25+ psi tire pressure however. I cut off the rubber tire valve stem and replaced it with an original metal valve stem and that fixed the leak.

Brad in Maryland

[Bob Johnson]

I replaced the valve core to see if that is the problem. I tried 4 different cores. I put a clear plastic tube over the valve stem and filled it with water. I put in 40 lbs of air pressure. Each core produced bubbles. I used long and short cores. I made sure the cores were tightened down hard. All of the cores produced bubbles. One of the long cores leaked so much that I could put my finger over the end and pressure would build up in seconds. The core currently in the valve might be OK. The picture below shows the air bubble produced after 30 mins. I will leave the plastic tube on it for awhile to see if any more air leaks out.
Bob

[Bob Johnson]

Here is a picture of the air bubble that took 12 hours to produce. I measured it at about 0.85 cm. The volume of that bubble would then be 2.6 cc. So we are looking at about 5 cc of air lost per day. What is the volume of the inner tube. I calculated 6800 cc (6.8 liters). However the air pressure in the tube was 40 psi (I made it high to force the leak). That would then be about 18,000 cc at standard pressure. 5 cc per day makes about 1800 cc per year. That results in a 10% air loss in one year. not a problem? Your calculations may vary.



Bob

[katy]

The picture below shows the air bubble produced after 30 mins.

Here is a picture of the air bubble that took 12 hours to produce.

What pictures? I don't see any pictures.

[Bob Johnson]

Some browsers or service providers block pictures from my domain (www.modelahouse.com). I do not know why. Click on this www.modelahouse.com to see if you can get to my domain.

Or click on this link to see the picture.
http://www.modelahouse.com/images/valve-core-leak02.jpg



Bob