Valve caps on wheels

[Griffoun]

Driving to work this morning and the Nissan Murano warned me about flat tire(s). The monitor shows tire pressures were at 27psi, and the recommended psi is 33. Then I found two valve caps were gone, and the remaining two were very loose, pretty close to coming out.

Q1: Did the caps come out due to driving condition (heating / cooling on the tires causing psi to change) and weather? I'm well aware of lower tire pressure when fall and winter comes (it cooled down quite a bit in Chicago recently), just didn't expect losing so much.

Q2: Are there any differences to the tires if I use metal or plastic valve caps? I wanted to get the metal ones from Walmart (since there's one close to work) but only the plastic ones are available

[Griffoun]

Here's what I found on the web, but then it's just one site's opinion...

http://www.techtirerepairs.com/tech_speak/Volume%2026%20Issue%202.pdf

PASSENGER VALVES
Valve Caps ***8211; most passenger valves are fitted with plastic valve caps. This is not an
acceptable practice for any valve. A metal valve cap must be fitted to every valve stem.
Plastic valve caps are only used to protect the valve stem threads during transportation
of the valve. The metal valve cap keeps out water and debris, as well as maintaining air
pressure in the event of a valve core failure. Plastic caps have a low temperature rating
of 0°F (-18°C), while metal caps have a lower temperature range for use in colder
climates.
Valve Cores ***8211; the valve core allows the air pressure within the tire and wheel
assembly to be adjusted. It must be in good working order with no debris within it.
Debris would not allow the core to seal properly. There are two types of cores used for
passenger valve stems; with the main difference being the temperature rating. A
standard valve core usually has a black seal with a temperature range of between -65°F
(-54°C) and 225°F (107°C). The high temperature core usually has a red seal and has a
temperature range of -65°F (-54°C) and 250°F (121°C) and is designed more for use in
truck applications.
Valve Stems ***8211; snap-in valve stems for passenger tires have a maximum air pressure
rating of 65 psi (4.5 bars). This will allow snap-in valves to be used in all passenger and
some light truck applications.
Proper rubber compound - All snap-in valve stems must be made with EPDM
synthetic rubber rather than natural rubber to meet SAE 1205 ***8211; 1206 ozone
requirements. EPDM rubber also has a broader temperature range than natural rubber
and will remain flexible in extremely cold weather.

[Sam Cogley]

I put machined aluminum caps on everything.

[Griffoun]

I put machined aluminum caps on everything.

and that's because...? :dunno:

[jcatral14]

and that's because...? :dunno:

Bling obviously :rofl:
Just put in valve caps plastic or otherwise. I don't think it makes a difference.

[Sam Cogley]

and that's because...? :dunno:

Look better against aluminum wheels and they're stronger.

[Griffoun]

Went to NTB after work and the guy there suggested plastic is better choice in case the metal is rusted... of course aluminum wouldn't be a problem... but he also mentioned wheels with pressure sensors require special caps and plastic wouldn't work. He then showed me some special caps with sensors which is plastic inside and metal on the outside, and told me to check with the auto parts shops or the dealer. Regardless, the 67 cents caps from Walmart does the job for now and doesn't show any interference with the tire pressure sensors...

Still need to find the right answer.

[mtbscott]

On my new MINI, they specifically warn against using metal valve stem caps, saying they will corrode/bond themselves to the aluminum stems of the TPMS sensors. They come with some mushroom shaped flat ones (the exact same ones as on new BMW's.) Don't know for sure but I doubt you lose much pressure even without a valve cap, I never run them on my tubeless bicycle tires and don't notice any significant air loss over time.

[jcatral14]

Why you may not want metal caps...:eek:

http://www.bimmerfest.com/forums/showthread.php?t=311326

[Griffoun]

Why you may not want metal caps...:eek:

http://www.bimmerfest.com/forums/showthread.php?t=311326

Thanks for the link!

[Sam Cogley]

Why you may not want metal caps...:eek:

http://www.bimmerfest.com/forums/showthread.php?t=311326

I've been using them for years on various vehicles and have never had one get stuck. I have had to yank a few plastic caps off with pliers, though.