Symptoms
- Tire loses pressure slowly with no visible puncture
- Valve stem looks cracked, discolored, or brittle
- Hissing sound near the valve when checking pressure
Likely causes
- CommonRubber valve stem aging and crackingStandard rubber stems typically last about the same lifespan as the tire but can crack sooner from sun and ozone exposure.
- CommonValve cap missing, allowing debris to damage the valve coreA missing cap exposes the valve core to dirt and moisture, which can cause slow leaks.
- PossibleLoose or worn valve coreThe tiny valve core inside the stem can loosen or wear out independent of the stem itself.
What to do
- Spray a little soapy water around the valve stem and cap while the tire is inflated; steady bubbles indicate a leak at that spot.
- Check the valve cap is present and snug, since it keeps debris out of the valve core.
- Try tightening the valve core with a valve core tool if the leak seems to be from the core rather than the stem itself.
- If the rubber stem itself looks cracked or the leak continues after tightening the core, the stem needs replacement.
- Valve stem replacement typically requires dismounting the tire briefly, so it's usually done at a tire shop rather than at home.
- Replace valve stems on all tires when getting new tires installed, since it's a minor added cost compared to doing it separately later.
Tools and parts
- Soapy water spray bottle
- Valve core tool (optional)
Replacement rubber valve stemSearch: “tire valve stem replacement”
When to call a pro
If you can't find the source of a slow leak yourself, a tire shop can submerge the tire in water to spot bubbles from even tiny leaks.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.