Mystery Flat?

This morning (Tuesday), I went out to the garage and noticed that one of my front tires was almost flat. I checked the pressure and, sure enough, measured only 8 psi.

On Saturday, I checked the pressure on a couple of the cars. This tire was at about 26 and I raised it to 29. On Sunday, I drove the car for about an hour and didn't notice a problem.

So I removed the tire and couldn't find a nail or any other problem. I removed the valve and it looked fine so I put it back in. Then I inflated it to 32 and submerged it in a tub of water. No bubbles anywhere, tread, bead, or valve stem. It has held pressure now for 12 hours. I'm wondering if perhaps the valve pin didn't reseat properly on Saturday when I added air. Does this sound like a reasonable explanation?

My guess is a bad stem - keep an eye on it.

I had that happen once. Replaced the valve stem and all was wall thereafter.

I had a little tiny nail in one of my tires and didn't see anything but sure enough it needed a patch.

No bubbles, though, and it's holding air now.

I thought you said mystery Fiat. Is it an alloy wheel? I have a couple on my e30 that will mysteriously lose air, but then be okay for weeks or months. I think it's just a case of corrosion on the rim, and I happen to go around a corner a little too fast or hit a bump.

I've had several alloys lose air/ flats over the years at the bead or stem. A little corrosion of the alloy will do it. I have bead sealer applied on all street alloys now.

The worst case was when I ran on a BFG/ AT, ruined the sidewall.... that berkeleying hurt

It's an alloy, but it's like new, and again, no bubbles.

I've had the same thing on a bead, same 4 tires for the last 2 years, had one go flat every 3 weeks, finally had it dismounted/remounted, been fine for the last year...

The 'no bubbles' bit may be true while the wheel is submerged without any load applied, but if it were possible to add some load to the tire as if it were mounted/being driven on, perhaps you would see a different result.

Beat the crap out of whichever of your kids is the most likely to be curious enough to play with the valve stem

Giant Purple Snorklewacker wrote: Beat the crap out of whichever of your kids is the most likely to be curious enough to play with the valve stem

They're in the clear. One is far too young and the other, far too lazy.

My Liberty had three wheels/tires that regularly lost air. Never could find a leak. Just got used to checking weekly or before a trip.

There've been issues with failures in some valve stems from China going south.

These were mounted by Tire Rack, so I'm pretty sure that the stems are okay. I ran into that problem with trailer tires, though. The stems dry rotted in less than a year.

Check your rims

My Sebring had a very small hair line crack the eye couldnt see and it leaked for years and would drive me crazy!