Most valve stem suppliers say tire dealers should always replace should always replace the valve stem when replacing a tire. Valve stems should also be inspected anytime a tire is balanced, repaired or dismounter. A tire valve stem that is cracked, damaged or leaking must be replaced.
Tire Valve Stem Replacement
Before removing a valve stem, determine if the vehicle is equipped with valve-stem mounted Tire Pressure Mounting Sensors (TPMS). Attempting to pull out a valve stem with an internal TPMPS sensor will destroy the sensor (which can be very expensive to replace). On TPMS applications the tire must be deflated and separated from the rim or dismounted to remove the valve stem.
Before installing a new valve stem, inspect the hole in the rim for nicks, burrs, corrosion or other roughness that damage the new valve or prevent a leak-free seal. Most valve stems are coated at the factory to maintain their appearance and to easy installation. If a lubricant is used, don't not use a petroleum-based product (rubber absorbs oil). Carefully pull the valve into the hole and make sure it is properly seated.
On some light truck application, special "high pressure" valve stems may be required (refer to the pressure rating of the tire). Most passenger c ar and light truck valve stems are only rated ot maximum of 65 psi. so if the vehicle has high load tire it will require high-pressure rated valve stems.
On TPMS applications, the valve stem may have a seal and external nut at the base to hold it in place. This nut must be tightened to specifications with an inch-lb. Wrench. Overtightening can damager the valve stem and sensor.
Never assume the old valve is the corrent one for the application because it may hve been replaced previously. Use a replacement valve stem that corrently matches the type of wheel and vehicle application. Many allloy Wheels require a clamp-in style valve stem with a threaded metal nut.
On heavey-duty trucks, make sure the valve grommet is the correct size for the hole in the wheel, and that the valve stem is properly positioned balance and to allow easy air pressure checks.
Finally, make sure the valve core is fully seated and dones not leak air once the tire have been mounted and inflated. And always install the cap to keep out dirt and moisture.