Can't find air leak

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Quattro Pete

Quattro Pete

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Oct 30, 2002
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One of the tires on wife's C300 is slowly leaking air. It went from 32 PSI to 20 PSI is 3 days. I thought it was a nail in the tread. I took it to Firestone today and they couldn't find a leak. They did not find any nails/screws. They checked the valve. Nothing. What the heck?

They went ahead and replace the valve core just in case, since it was the least expensive first thing to try. I guess I'll see in a few days if it made any difference.

I'm thinking there probably still is a nail/screw in there somewhere but they just missed it.

The rims are factory 17" alloys and appear to be in good shape visually, however, this particular rim is slightly bent. It does not cause any vibration on the steering wheel and it's been bent for years, while this leak only developed within the last month.
 
Alloy rims can crack if they are hit too hard or bent too much. While it may not have happened right away, the rim could have been weakened then cracked in the recent abnormally cold weather. Its your wifes car and somethings up. You know the alloy rim took a pretty good hit. Replace it rather than risk a blowout. Junkyard maybe.
 
That's a massive leak...take it somewhere else and get a second opinion! As you mentioned..."I'm thinking there probably still is a nail/screw in there somewhere but they just missed it."
 
Originally Posted By: JamesBond
There have been some big temp changes in IL during the last week, could that have contributed?

No. The measurement was taken in the garage in roughly the same ambient temp.
 
I just tried to remove the wheel so that I could inspect the tread. Sadly, the Firestone grease monkeys have tightened the lugs so much that I could not unscrew them even when I jumped on the lug wrench. Sigh....
 
I almost agree with Chris142. Use soapy water, but don't overinflate. The slower the leak the more money the tire store is losing by trying to find it so they give up pretty quickly.

Drop the pressure to the low to mid 20s (higher pressure may hide a bead leak) and coat the entire tire and wheel assembly (rims can and do crack - especially on MB and BMW) with soapy water. Let it sit for a few minutes and inspect it thoroughly. If you see any white spots show up, look more closely. Keep in mind that if you have an existing tire repair or a crack that you believe isn't leaking it is quite possible that the repair or crack will leak intermittently.
 
Originally Posted By: Quattro Pete
I just tried to remove the wheel so that I could inspect the tread. Sadly, the Firestone grease monkeys have tightened the lugs so much that I could not unscrew them even when I jumped on the lug wrench. Sigh....



I'm pretty sure that's a punishable offence at a Firestone. No doubt they'll be happy to loosen and re-torque the lugs immediately when you can find the time to stop by.
 
Originally Posted By: Quattro Pete
I just tried to remove the wheel so that I could inspect the tread. Sadly, the Firestone grease monkeys have tightened the lugs so much that I could not unscrew them even when I jumped on the lug wrench. Sigh....


Aren't you glad you found that out now rather than when you had a really flat tire.

For your soapy water, I like dish liquid (not dishwasher soap). I have not tried adding glycerine. http://www.ehow.com/how_5993424_make-leak_detection-soap.html
 
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Take the tire off. Carefully inspect the tread for foreign matter (stones, screws, nails, glass, or some other surprise). Remove anything suspicious from the tread and apply soapy water. Look for bubbles.

Lay the tire flat, backside up. Drizzle some soapy water on the bead. Wait a few minutes (drink some coffee) and then look for bubbles. A good leak will make a patch of foam.

Flip the tire, remove the valve cap. Drizzle soapy water on the bead, where the valve stem goes in the rim and over the valve core. Wait a few minutes and look for bubbles.

If that doesn't work, the tire will have to go in a water tub (which you probably don't have).

A 12 PSI drop in 3 days is a substantial leak, it should make itself apparent.
 
Thanks for the advice, guys. I'd love to get that sucker off and inspect the tread and do the soapy water test, but it'll have to wait until I can make a trip back to Firestone to loosen the lugnuts first, or until I can find a lug wrench with a longer arm to step on.
 
Originally Posted By: Quattro Pete
Thanks for the advice, guys. I'd love to get that sucker off and inspect the tread and do the soapy water test, but it'll have to wait until I can make a trip back to Firestone to loosen the lugnuts first, or until I can find a lug wrench with a longer arm to step on.


the 9.99$ 18" harbor freight breaker bar is always good
smile.gif

or 25" for 11.99

then buy a 1.49$ socket to go with it

I have one in every car.

some good advice in here.

I usually make a pitcher of warm water.. stir in some dish soap try not to agitate it.

then pour on tire you can do it on the car, but abit easier to do it off car.
4#/day is a pretty big leak.
 
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Thanks. That breaker bar sounds like a good tool to have. Does HF sell individual sockets? I need a 17mm one and don't see it on their website. I have one at home in IL, but I'm not there now.
 
they did sell individual sockets but some are phasing that out.

If its phased out AAP or AZ will sell a 17mm for 3.49$ or so usually.
 
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I do, at our primary home. But I won't be back there for the next 2-3 weeks.

Maybe if I weighed 300 lbs, that wouldn't have been a problem.
smile.gif
 
Originally Posted By: Quattro Pete
Thanks. That breaker bar sounds like a good tool to have. Does HF sell individual sockets? I need a 17mm one and don't see it on their website. I have one at home in IL, but I'm not there now.


This kit might be overkill but I have it and it's cool to have.

image_13728.jpg
 
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