dandelos

Lost the two rear caps and since then the left rear tire has been losing pressure too quickly (i.e. 45 to 37 drop within a week). I know the caps aren't really supposed to prevent pressure loss as much as keep the stem valve clear of mud and debris, but who knows. Might be a nail, though the tires are worn and are due to be changed anytime now anyway.

And writing this it just occurred to me that I could transfer the front caps to the rear to test the pressure loss theory out. Oh well...

In any case, does anyone have any recommendations for good and cheap tire stem valve caps that I can get? I read that metal isn't recommended, as different alloys might bond over time, so I should stick to plastic?

Thanks in advance!

Frank 993 C4S

You could not tighten the valve caps tight enough in order to keep 30+ psi in the tire so it's probably a nail. On TPMS systems use plastic caps only.

XR4Tim

I have seen ice form in valve stems, preventing them from sealing all the way. This is a possibility with your cap missing if you're in a cold climate.

Renn 951

Make sure the valve core is screwed in tight. With the cap gone, some foreign object might have gotten in the stem and loosened the core just a bit.

dandelos

Noted, thanks!

Moderate SoCal weather here, and car is garaged, so I doubt ice is a factor. Thanks, though.

Will check, thanks!

hahnmgh63

If you were between the freezing temps drop and you had checked the tire relatively warm and now again with real cold temps that you account for some of it, but of course it would affect all tires equally.

dryadsdad

Caps DO prevent pressure loss. Replace with metal and see if that makes a difference.

DWPC

Troll or uber-cheapskate?

dandelos

Me? I can be a troll sometimes and am not ashamed to admit that I'm most certainly a cheapskate (or perhaps to be PC, a deal finder). But it was an honest-to-goodness question/OP. I've seen several caps being sold on Amazon and eBay, and while cost is always a factor for me, quality is also a significant consideration, especially when it comes to our cars. I don't want to buy any ol' set of caps just because they are only a few bucks without being convinced they're the right ones for our needs (durable, won't cause additional issues, etc). So if anyone has any specific cap recommendations I'm still all eyes+ears.

DWPC

Caps protect the stem valve from dirt/debris; the "seal" they provide may help slowing loss in a complete valve failure. Replace the stem valve at a local tire store.