SOLVED - Unexplained sudden loss of tire pressure every few months

[AdamIsAdam]

All of a sudden, while driving on the highway, my front left tire went from reading 34 PSI to 24 PSI for the second time in 4 months. Why?

(NOTE: My car's tire pressure readings consistently display 2 PSI higher than on my three, high quality gauges, so I run them at an indicated 34 PSI.)


More info:
Today, after driving for about 20 minutes on the highway in 35* weather, the front left tire dropped to 24psi. BUT, yesterday I had the car out for a 20 mile loop and checked all 4 tires, and they were all at 34psi. My Longacre gauge confirmed the 24psi reading as I added air at a gas station. The rest of the day it was fine. (Ironically, both the car and my gauge both said 24psi.)

This same thing happened once before about 3-4 months ago, from 34 to 24 psi on the highway in the front left tire, but once corrected, was fine until today.

It's not the electronics of the car since I confirmed the low pressure reading with a known, good gauge.

It's not ambient temp related since the other three tires are fine.

I don't see anything wrong with the tire, like a nail (but I have not removed the wheel to really check).

Any thoughts? Remember, it's not a slow leak, but rather a sudden 10 PSI drop that only happened twice this year.

(Pic from today just for fun.)

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[AdamIsAdam]

No replies? hmm. Assuming it's not the obvious, which I'll have checked out by either a good tire shop or dealer, I did read somewhere that very slight cracks or VERY small cuts in the tread could hold air fine until they reach a certain temp and thus PSI. Which could explain why the tire holds air in storage and during most drives.

But I posted here because I was wondering if anyone else had strange issues that may be caused by the tire-to-wheel mount or a faulty valve.

 

[Docscurlock]

Something is causing a loss of air, I've never had that problem, have you tried running nitrogen? Thats what I use in mine, not as touchy with temp issues and apparently N2 is a larger molocule and thus less prone to microleaks.

 

[Hack]

Air is 80% nitrogen and the difference between oxygen and nitrogen does not explain this.

To the OP - I'm not sure what the cause of your seemingly intermittent leak is. I've never had a tire that sealed most of the time but occasionally leaked. I suppose it could be the valve stem or something.

 

[Furiousone]

I know that the TPS sensors seal/stem can be prone to very slow leaks, but usually it has to do with temp changes(expansion/contraction), which you stated is not an issue. I'd take the wheel off, spray liberally with soapy water and see if there is anything out of the ordinary. This is what a tire shop would do.

 

[Tank]

Valve stem or bead issue..

Or maybe a crazy puncture???

 

[Docscurlock]

Air is 80% nitrogen and the difference between oxygen and nitrogen does not explain this.

To the OP - I'm not sure what the cause of your seemingly intermittent leak is. I've never had a tire that sealed most of the time but occasionally leaked. I suppose it could be the valve stem or something.

Exactly, he is leaking out the 20%
On a serious note, any trips off the side of the road, check for grass or dirt in the tire bead?

 

[JR369]

Just faced this situation about a month ago or so. While on the Interstate my pressure in the drivers front went from 35 to 21. Got the warning light, so I pulled off at the next exit. Sure enough, I found a screw. Got it to the nearest discount tire. Thankfully they had a touchless for my CF wheel. At first they didn't want to touch the tire because they said there is no tread depth left. My R only had 1100 miles on it Lol. I had to explain that to them. I convinced them to repair it with a plug. Been solid since. Two things on my mind now. Replacing that tire because in no way can it be trusted and getting a spare set up.

I think when I was driving the car and thru a dip or something, maybe a bump in the road, the screw would breach the inner wall and air would escape. The screw was not very long.

 

[Hack]

Exactly, he is leaking out the 20%
On a serious note, any trips off the side of the road, check for grass or dirt in the tire bead?

20% wouldn't get you down from 34 psi to 24 psi. So even if every single last O2 molecule went missing the pressure wouldn't go down that much. And then the first time you filled up the remainder with air again there would only be 4% oxygen in the tire (20% of the 20% that leaked out). So if O2 really leaked out of the tire it would only take a few times topping off the tire to get mostly N2 in there.

I realize you are joking but I'm too pedantic to let it go.

 

[lightrules]

really weird. my wife and I are re-watching "lost" with my older two kids right now, and your issue seems like a good episode.

so it's not a nail, it's not your TPMS sensor, really strange.

 

[JAJ]

No replies? hmm. Assuming it's not the obvious, which I'll have checked out by either a good tire shop or dealer, I did read somewhere that very slight cracks or VERY small cuts in the tread could hold air fine until they reach a certain temp and thus PSI. Which could explain why the tire holds air in storage and during most drives.

But I posted here because I was wondering if anyone else had strange issues that may be caused by the tire-to-wheel mount or a faulty valve.

You've got a nail or a screw in the tread. It could be a loose bead, but when I had the factory bead leak on my 2014 GT500 (a batch of tires were installed on front rims by the supplier with a part number sticker stuck between the bead and the rim), it was a slow drop in pressure.

If it's a nail, it could be hard to find because the head's worn off and now all you can see is a little dot.

 

[302@12psi]

You either have a nail, a valve stem issue, or a bead seal issue. I've seen some tires with stickers on the bead that will cause a leak. Take it to a GOOD tire place and have them put some soapy water around the bead/valve stem first. After a visual inspection for nails.

If you want to do it at home just take the wheel off, look for a nail, and if found get it repaired. If you do see anything in the tread then lay it flat and put a soapy water mix over the valve stem. If it isn't that go around the front and rear of the bead and look for small bubbles.

 

[Deleted member 35644]

A friend of mine with a 2005 G35 coupe had this happen several times, and they finally discovered a crack in her wheel . Wasn't in an obvious place so it took them a while of blaming the tire, replacing the tire, and still having a leak.

 

[Docscurlock]

20% wouldn't get you down from 34 psi to 24 psi. So even if every single last O2 molecule went missing the pressure wouldn't go down that much. And then the first time you filled up the remainder with air again there would only be 4% oxygen in the tire (20% of the 20% that leaked out). So if O2 really leaked out of the tire it would only take a few times topping off the tire to get mostly N2 in there.

I realize you are joking but I'm too pedantic to let it go.

So, he lost 29% of his "air" pressure, By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. So roughly 22% of air is not nitrogen depending on how far away from sea level he lives and with water vapor being variable with the humidity level. We only have to account for 6-7% of the air now or basically 2lbs of pressure. I'm betting it's probably a nail or screw or something in the tire bead but this is a much more fun theory to play with.

 

[Hack]

So, he lost 29% of his "air" pressure, By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. So roughly 22% of air is not nitrogen depending on how far away from sea level he lives and with water vapor being variable with the humidity level. We only have to account for 6-7% of the air now or basically 2lbs of pressure. I'm betting it's probably a nail or screw or something in the tire bead but this is a much more fun theory to play with.

Yeah - I didn't want to get into molecular weight, water vapor, etc. Not quite that pedantic, I guess.

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