I suspect this may be a dumb question but here goes. I've had a tire that'* been leaking air for about three years now. I've had numerous tire places look at it and I've been told it'* not leaking, or at least they can't find the leak. Well, I'm getting new tires all around and if it'* the tire,.... problem solved. But I still must ask the question ... can air leak from someplace other than the tire (or valve stem) such as the pressure monitoring system? Thanks.

Not with the Bonneville. The system works by looking for a single wheel which turns at a different rate (somewhat simplified explanation). This would indicate the pressure in the one tire is different than the others. Because the system uses the wheel speed sensors, there is no way this can cause a leak. It may be possible with the newer generation where a pressure tranducer exists in each tire and is part of the valve stem, but not our cars.

Could there possibly be an explanation as to why know one could ever find the leak (beyond incompetence)? I think three different places over the years looked at it. Dealer, tire center (two times) and my mechanic. The leak was very slow at first, but more recently, it appears to have gotten much worse. Could a crack in the inside of the wheel a possibility. Again, with the install of new tires this all may be a moot point.

You know, I have the same problem. All of my tires are within 3 psi of each other, yet every time my car sits and gets cold again, I have to reset my Tire Pressure Moniter on the dash. This has only started to happen recently for me.

Soo.... even a possible early sign of a failing wheel speed sensor?

To find a leak, I suggest total immersion in a tank--I used bathtub and filled as high as possible then just watched for half an hour to see if a bubble emerged. Then I turned the whee and checked another region.

Resetting tire monitor: are you resetting it while moving or while sitting?

Interesting thought. I may or may not have a failing wheel speed sensor. But if I let the tire go until my tire pressure monitor tells me to check tire pressure, the leaking tire only has about 15 lbs of pressure in it. More recently, I put about 8 lbs of air into it, and only then did the tire pressure monitor tell me to check the pressure. With all this said, my original question still stands. Can anything other than the tire and or valve stem be leaking (crack in wheel).

Generally, there'* not a whole lot of different way'* for air to leak:

Bad seat, in which the tire just needs to be reset onto the wheel, mounted, and balanced.

Bad valve stem, but that'* easily catchable.

There'* no nails or anything in the tire itself? Sometimes you can only find these by looking at the inside of the tire.

Cracked wheel can cause it, but you'd probably have more issue'* than air just leaking in this situation.

That'* good to know. I'll talk to the tire center before they put on the new tires and ask them to inspect the tire and wheel. It would be good to know the culprit. I guess in the back of my mind I'm fearful that a month after I put on new tires, I'm going to find one with only 15 lbs of pressure!

There are some rims like aluminum that can have porous areas which allow air to seep. That'* what I was looking for with the water test as well.

I have had small nails in tires that are hard to find. The water check didn't detect any air bubbles, but when the tire rolls the tread flexes and the nail (brad) would let air out around the flexed area. Then if the car is parked with the nail at the flexed area the air leaks out faster while sitting.

Crap, I knew I was forgetting something Aluminum rims are notorious for this. The porous metal gets worse over time, allowing more and more air to escape.

My dad'* 95 Impala is notorious for this. Almost every winter, he has walked out to a flat tire. Fortunately he doesn't drive it much anymore, except for a nice weekend, or doing errands in the summer.