While looking at the valve stem, make sure the core is free of dirt and debris, which could cause interference with the valve function. Once you’ve assured yourself that the core is working properly, the only other caution is not to overtighten the valve core when you re-install it. This is particularly true with metal valve stems. You want the gasket seal to be tight, but you don’t want to ruin the seal by overtightening it. The same holds true with rubber valve stems, but they tend to be a bit more forgiving.
As a general rule, use the shortest valve stem possible. A longer stem is easier to get knocked off. If the owner of a vehicle is a fast driver, centrifugal forces occurring at high speed can cause a longer valve stem to bend and lose air.
Always check for signs of corrosion around the wheel’s valve stem hole, especially on alloy wheels with metal valve stems where the wheel is made of one metal and the stem from another. If you see any white residue around the gasket seal, remove the stem and replace either the seal or the whole valve stem. Also, inspect the valve hole for for nicks, burrs, or other roughness that could damage a new stem or prevent a leak-free seal.
Another safety step to improve the odds against air loss involves a self-sealing valve stem cap that has been securely screwed down on the valve stem itself. This way, even if the valve core leaks, the air inside the tire will be contained by the cap. Keep in mind that a good valve cap costs pennies, but it can save a great deal of trouble.
Never assume the old valve stem is the correct one for the application, since it may have been previously replaced. Always use a replacement valve stem that correctly matches the application. For example, many alloy wheels require a clamp-in type valve stem with a threaded metal nut.
Also, be sure when you are removing a valve stem you know whether the vehicle is equipped with TPMS. Attempting to pull out a valve stem with an internal TPMS sensor will destroy the sensor, resulting in a very expensive replacement. On TPMS applications, the tire must be deflated and dismounted from the wheel to remove the valve stem.
