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My car is a 2007 model FIAT Albea 1.3 liter 4-door saloon. I think it might be the "fire" version. Made (assembled) in Turkey. I use it 6 months a year but 4-5 weeks at a time. When it's stored/parked at my friend's place he keeps the engine running but does not drive the car. Invariably he has to replace a wheel, put on spare, take the flat tyre to a repair shop only to be told that there's no puncture! The tire goes flat "for no reason" but why?

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Did you check the condition of the wheel that leaks? Air could leak out through a tiny gap between the rim and the tyre. – I have no idea what I'm doing Mar 17 at 16:33
    
is it always the same wheel? – Erik vanDoren Mar 17 at 17:19
    
I thought the fiat tag was a typo of flat until I read the question text. – March Ho Mar 17 at 22:40
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In addition to the answers, I would find a new 'repairer' as the one your friend is using is plainly of little help. – Paddy Mar 18 at 7:34
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Your friend keeps the engine running while storing the car? Why does he do that? – Jamie Vicary Mar 18 at 15:16

Your wheel is obviously leaking somewhere.

There are a few places that you can have a leak related to the wheel

  • The Schrader Valve - The schrader valve within the valve stem where you refill the air can be bad and require replacement.

  • The valve stem - The valve stem where the schrader valve is in can have a bad a seal on the rim

  • Tire Pressure Sensor - I didn't look up if you have one but many cars do have a tire pressure sensor. You can have a bad seal on your wheel.

  • Tire Bead - All around your tire where the inside diameter of it meets your wheel requires a nice smooth surface. You can have leaks here.

Overall

Any damage to the surface of any of the above points can cause a leak. It could have been a tire change from a careless tire worker. A good scratch along the bead, a pair of pliers replacing the valve stem and a nick in the valve stem hole.

You may need a new rim but you would have to pull the wheel and remove the tire, valve stem and pressure sensor to give it a good inspection to determine where the leak is and see if you can fix it with some sandpaper if it's a bur on a sealing surface of your wheel.

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Adding a little flavor to this answer: I just took my summer tires down off the rack after a while winter. All of them were still close to operating pressure (lost maybe 2 psi over three months). – Bob Cross Mar 18 at 10:41
    
@BobCross I have a few sets of rims and tires for some of my bikes and they seem to lose pressure at about the same rate you just stated. – DucatiKiller Mar 18 at 18:52
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This is reminding me of my old impreza. I had gotten into a small accident in the winter time (no collision) that involved a wheel hitting the curb. There was no visible damage, but from that point on that wheel would need air more regularly than the rest. The problem persisted after getting new tires, at which point I had to conclude the rim must be ever so slightly damaged, but not enough to be visible. – BooleanCheese Mar 18 at 18:56

One way to determine where the tire / wheel is leaking, is to make a solution of soapy water and put it in a spray bottle. Take the wheel off the car, and coat the tire and wheel on every surface with the soapy water. The place where the bubbles are active is your leak. I have no doubt that one of the places @DucatiKiller mentioned will be the problem.

Hope that helps!

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The best way to find a slow leak is to put the tire under water and look for bubbles. Try to find a tub big enough to cover the sidewall with the tire standing up. Pump the tire up to about 35 PSI, and put the tire in the water. rotate it slowly and watch for bubbles.

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Two issues here:

  1. The wheel rims might be rusted or encrusted with dirt, which prevents a good seal between the wheel and the tire. In that case, the tires should be taken off and the wheel rims carefully cleaned, de-rusted and sanded smooth. The tires should then be mounted and sealed to the rim. There are various techniques for this, each with their own pros and cons. Google.

  2. Tires are filled with air under pressure. Air consists of about 78% nitrogen, 20% oxygen and a few other gasses. Oxygen molecules are small enough that they can actually pass through rubber -- slowly, but steadily. In addition, oxygen is very reactive -- it will corrode anything it can. Then there's also the moisture in air, which will hasten any corrosion process. Airplanes and racing cars therefor have tires filled with nitrogen. You will need to find a service station that has pressurized nitrogen. The nitrogen molecule-pairs (N2) are too big to pass through the tire walls (unless the rubber is falling apart, of course) and it does not contain moisture. In addition, pure nitrogen expands and contracts less than air does in the usual temperature ranges of most climates. I had my tires deflated and filled with nitrogen at a service shop that does oil changes and the like. It cost only 16 euros (4 euro per tire).

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If a tyre loses that much air over such a short time span, I wouldn't throw good money after the bad, letting the tyre leak pure nitrogen. – Alexander Mar 18 at 13:12
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That 16 euros is about 15 euros pure profit for the shop - fools and their money are soon parted! Racing car and aircraft tires have much more severe working conditions than typical road cars. For example you don't chill your car tires down to below -50C when you go for a drive, and then heat them to 50 degrees above the ground-level air temperature when you hit the brakes, but that's what happens to the tires on a commercial passenger aircraft, on every leg of a flight. – alephzero Mar 19 at 2:58
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I think you're confusing "pure profit" with "money to pay for rent, taxes, healthcare and salaries". – Eloy Mar 19 at 14:33

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