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How can you tell whether the valve is leaking air?
You can tell whether the valve is leaking air with the soapy water test: with the tyre at pressure, remove the cap and wet the valve. Bubbles at the tip indicate a leak from the internal valve core; bubbles at the base, where the valve enters the rim, indicate a leak from the valve body or its seat.
Other clues: the tyre goes down slowly with no visible holes, or you hear a faint hiss when you move the valve with your finger. The full test procedure is in slow puncture: how to find the hole.
Why does the valve leak air?
The valve leaks air mainly because of wear, dirt or mechanical damage.
- Loose or dirty valve core: the small internal mechanism doesn't close properly.
- Aged rubber stem: rubber valves crack with time and exposure to the weather.
- Knocks: hitting a kerb or going through a brush car wash can bend or crack the valve.
- Missing cap: dust and water get into the valve and compromise its seal.
- Corrosion: metal valves, such as those with a TPMS sensor, can corrode.
Rubber or metal valve: what's the difference?
The main difference is in their construction and how they're replaced.
| Rubber valve (snap-in) | Metal valve / with TPMS sensor | |
|---|---|---|
| How common | Very common on cars without direct TPMS | Common on cars with direct TPMS and on some rims |
| Fixing | Pushed into the hole in the rim | Secured with a nut and seals |
| Typical wear | Cracking of the rubber stem | Seals, corrosion, loose nut |
| Replacement | Requires the tyre to be removed | Requires the tyre to be removed and the sensor to be handled carefully |
For how the sensors work, see the guide to the tyre pressure warning light.
What should you do if the valve is leaking?
If the valve is leaking, the solution depends on where the leak is.
- If it's leaking from the tip, it's often enough to have the internal valve core tightened or replaced: it's a quick job.
- If it's leaking from the base or the valve is cracked, the valve must be replaced: the tyre needs to be removed from the rim.
- On valves with a TPMS sensor, replacement involves seals or parts of the valve: it must be done with suitable equipment.
In the meantime, keep the tyre at the correct pressure and don't drive if it goes down quickly.
Does the valve cap matter?
Yes: the cap protects the valve from dust, water and dirt, which can stop the valve core from closing properly. It isn't what holds the air in, but it protects the mechanism that does.
If it's missing, replace it: it's a cheap, easy-to-find spare part. On metal valves use suitable caps, because some materials can encourage corrosion after prolonged contact.
Leaking valve in Milan?
If in Milan or the surrounding province the tyre keeps going down because of a faulty valve, SOS Tyre comes out 24/7, in 30 minutes on average, to wherever the vehicle is. Call +39 377 326 0999 or read the page on a deflated tyre.
Frequently asked questions
Can I tighten the valve core myself?
It's possible with a special valve core tool, but it needs a delicate touch: if you overtighten it or unscrew it by mistake, the tyre will go down all at once. If you don't have the tool or aren't confident, have a tyre specialist do it: it's a quick job.
When is it worth replacing the tyre valves?
Many tyre specialists recommend replacing rubber valves when fitting new tyres, because they age along with them. For valves with a TPMS sensor, the seals and sealing components are usually replaced. Ask the technician at your next tyre change.
Does a bent valve always need replacing?
Generally yes: a bent valve or one with a marked rubber stem can crack and suddenly lose air, especially at speed. If you notice the valve is tilted or damaged after a knock or a car wash, have it checked even if it isn't leaking at the moment.
Does the TPMS sensor break if the valve leaks?
Not necessarily, but a leak from a TPMS sensor valve may indicate worn seals or corrosion, which need to be dealt with to avoid damaging the sensor. During the job the sensor must be handled carefully and, on some vehicles, a relearn procedure may be needed.