[doro6529]

Plastic caps came OEM on both my Niros. Besides being cheaper quite possibly the reason to use plastic not metal was two fold. Metal, being substantially heavier, places bending and vibration stresses during rotation on the stem and TPMS, also metal can possibly interfere with the transmission of the signal from the sensor transmitter to the receiver.

But maybe most importantly the cap is in no way meant to hold tire pressure from leaking out. They are made to keep the valve that's inside the stem that is designed to hold pressure clean and clear of foreign matter, dirt, mud, ice, salt, so tighten lightly only. The plastic ones have done that brilliantly from 0°F to 100°F in my personal experience.

Putting pliers on a stem can put it out of round.
Truck owner asks, "How does a new tire go flat?" Smart a$$ truck driver, "Pssssssssssssssss....".

One other thing tires will suffer degradation from wear, heat cycles, from UV, they will start to leak through sidewall cracks and depending how hard you corner at the bead. You need to be able to get the **** caps off to keep up with the leakage that is until it pays to get a fresh set.

 

[SDeemer]

Metal, being substantially heavier, places bending and vibration stresses during rotation on the stem and TPMS, also metal can possibly interfere with the transmission of the signal from the sensor transmitter to the receiver.

I'm skeptical on both counts. Here are two valve caps:

In my hand, I can't feel a difference in weight between the two. I don't have access to a lab balance, but I do have a digital kitchen scale, which registers down to 1 gram. Neither was heavy enough to register by itself, and the two together registered as 1 gram. Because plastic (probably HDPE) is weaker than metal, more of it is needed, and the weight difference between the two seems negligible. Perhaps someone with access to a lab balance can measure with greater accuracy.

A metal cap is not going to have any RF shielding, as the valve stem has a metal core, and the TPMS sensor is inside the wheel, where it will be shielded by a large mass of aluminum or steel.

 

[atc98092]

Because of the Sun's heat in AZ, and Southwest, in general, plastic caps, will split and allow pressure drops!

Sorry, the caps themselves are not sealing in any pressure. There is a valve (schrader valve) within the stem that does the sealing. The cap does nothing but keep dirt out of the valve.

 

[JesusLover]

Plastic caps came OEM on both my Niros. Besides being cheaper quite possibly the reason to use plastic not metal was two fold. Metal, being substantially heavier, places bending and vibration stresses during rotation on the stem and TPMS, also metal can possibly interfere with the transmission of the signal from the sensor transmitter to the receiver.

But maybe most importantly the cap is in no way meant to hold tire pressure from leaking out. They are made to keep the valve that's inside the stem that is designed to hold pressure clean and clear of foreign matter, dirt, mud, ice, salt, so tighten lightly only. The plastic ones have done that brilliantly from 0°F to 100°F in my personal experience.

Putting pliers on a stem can put it out of round.
Truck owner asks, "How does a new tire go flat?" Smart a$$ truck driver, "Pssssssssssssssss....".

One other thing tires will suffer degradation from wear, heat cycles, from UV, they will start to leak through sidewall cracks and depending how hard you corner at the bead. You need to be able to get the **** caps off to keep up with the leakage that is until it pays to get a fresh set.

If your tires are that bad, you need to get them replaced: Crash in the making: But the again, I've see people running tires with the cords showing.
Low tire pressure is the number one cause of tire failures; PERIOD!
Caps are actually the secondary seal for the stem: just like in an HVAC system.
It was 115°F here in Phoenix Today. I've been using Metal caps for 25 to 30 years and I haven't had any issues with myTPMS on my cars, Motorhome, Honda, Yamaha, and BMW motorcycles, etc!
If you run Nitrogen in your tires, Metal Caps are recommended.

Sorry, the caps themselves are not sealing in any pressure. There is a valve (schrader valve) within the stem that does the sealing. The cap does nothing but keep dirt out of the valve.

The valve stem needle valve, also known as the valve core, is designed to seal itself using the air pressure inside the tire. This self-sealing mechanism is achieved through the spring-loaded pin within the valve core. When air pressure is applied to the tire, the spring-loaded pin moves into position, creating a seal that prevents air from escaping. The stem needle valves do need to be replaced as they develop seats in the rubber and if not seated in the same seat they tend to leak.
The cap, on the other hand, serves as a secondary seal: it is not just to keep debris from entering the valve core seal. It is designed to fit snugly over the valve stem and provides an additional barrier against air leakage. The cap’s seal is typically achieved through a rubber O-ring or grommet, which creates a tight fit around the valve stem. This secondary seal helps to prevent air from escaping even if the valve core becomes damaged or compromised.
More information:
Tire valve stem needle valves are called Schrader valves because they were invented and patented by August Schrader in 1891. August Schrader’s design for a tire valve valve, patented in the United States in 1893 (U.S. patent 0,495,064), featured a unique combination of a valve stem, valve core, and sealing mechanism.
In summary, tire valve stem needle valves are only called Schrader valves because they were invented and patented by August Schrader, a pioneer in valve technology, and his design became the industry standard for tire valves.
From the net:
Based on the provided search results, it’s clear that Schrader valve is a type of pneumatic tire valve, and not all tire valve stem needle valves are Schrader valves. There are other types of valves used on tires, including Presta and Dunlop valves.
Presta valves are used on narrower, high-performance rims, such as those found on road racing bicycles, and are characterized by their tapered design and lack of a mechanical check valve. They seal tightly based on air pressure alone and are easily extendable with adaptors.
Dunlop valves are also mentioned, although no specific details about their design or usage are provided. However, it’s implied that they differ from Schrader valves in terms of diameter (8 mm vs. 6 mm)
So, in summary: not all tire stem needle valve are Schrader needle Valves.
Have a blessed Day!

 

[atc98092]

The cap, on the other hand, serves as a secondary seal:

Not all plastic caps are equal. The majority of them had no seal whatsoever within the cap, and will not hold any air pressure. Yes, there certainly are caps out there that provide some level of sealing, but they are still not designed to hold 40 or more PSI for any length of time. I did have some aftermarket VW valve caps that were metal and had rubber seals inside, but they would still never be considered anything but an emergency cap to hopefully allow someone to get the car to a tire shop and get the Schrader valve replaced. And I realize there are different brands of valves for tire stems, but it's kind of like kleenex and aspirin becoming more of a generic name for a product. And since they all have to fit within the same tire stem for automotive purposes, it's rather immaterial what name is used.

 

[JesusLover]

Not all plastic caps are equal. The majority of them had no seal whatsoever within the cap, and will not hold any air pressure. Yes, there certainly are caps out there that provide some level of sealing, but they are still not designed to hold 40 or more PSI for any length of time. I did have some aftermarket VW valve caps that were metal and had rubber seals inside, but they would still never be considered anything but an emergency cap to hopefully allow someone to get the car to a tire shop and get the Schrader valve replaced. And I realize there are different brands of valves for tire stems, but it's kind of like kleenex and aspirin becoming more of a generic name for a product. And since they all have to fit within the same tire stem for automotive purposes, it's rather immaterial what name is used.

I am a Certified Technician working in the Automotive industry for over 50 years, I gave the correct information, when I wrote earlier. Then I even did a search to back it up and I quoted what was on the search and available from multiple sources. But then again it is hard to change someones mind that is not willing to admit he may just be in error! Do a search on your own. A stem cap is designed to act as a seal and backup in case of core valve failure or leakage, PERIOD!
I know that I spend a lot more time with tire maintenance, than the average vehicle owner, because of our traveling in our ministry to help people in RV Parks and campgrounds. People do not know the correct way to even know how much air to run in their RV's, and Truck tires, and most don't want to take the time to check their tires before each trip or during their trips.
I have metal caps on my 500HP Cummins Diesel Pusher 43ft motorhome's valve stems that have held 125lb on cores that had a leaks. I always test for core leaks, when I take caps off to check pressures in different climate locations and load conditions, to back up TPMS readings. My car trailer's dual axle runs 100 lbs tire pressure with metal Valve stem caps and TPMS with no transmitting issues. Our combined coach and trailer weight is over 60,000 and length of 65 ft, which we've travelled the US in, for over 20 years. So, I believe I know a little bit more than the average vehicle owner. Tires pressures are set according to weight on the axles and Temperatures at a mean temp of 65°. Car and Pickup truck tire pressures should be increased if heavily loaded to maximum pressures,located on the tire's sidewalls , to prevent tire failure.
Tire safety has been a BIG ISSUE in my Road helps ministry for over 30 plus years.
Have a nice day!

 

[atc98092]

A stem cap is designed to act as a seal and backup in case of core valve failure or leakage, PERIOD!

All I'm saying is there are differences in stem caps. Some absolutely will provide a decent air seal. But the basic plastic caps have no seal within them and will not hold pressure. I really don't think we're disagreeing about any point other than that. Bless you for your ministry.

 

[Techy]

I am a Certified Technician working in the Automotive industry for over 50 years, I gave the correct information, when I wrote earlier. Then I even did a search to back it up and I quoted what was on the search and available from multiple sources. But then again it is hard to change someones mind that is not willing to admit he may just be in error! Do a search on your own. A stem cap is designed to act as a seal and backup in case of core valve failure or leakage, PERIOD!

I too am a certified tech but only have 44 years under my belt.
A stem cap's main purpose is not to act as a backup in case of valve core failure and in the case of the plastic ones that don't have a rubber O-ring in side, they can't seal against a leak and are simply used to keep dirt from entering into the valve core and causing an eventual leak.
We don't have to change anyone's mind here. Everyone can provide their opinion and live within what they are comfortable with.
The OP was excellent in bringing to the forefront a problem with many of the metal caps and I hope people that have read through this thread, regularly check those metal caps (like when they check tire pressure monthly) because once they are seized on, it is not a good situation.

 

[Dovidan]

Who knew stuck valve caps would generate 28 + posts!
I'd love to hear if & how the OP resolved his problem!

 

[doro6529]

IIRC, Schraeder valves are actually a specific part that has a 'S' stamped into the end of the release plunger to differentiate it from your run of the cheap mill tire valve used in passenger car tires. It's made for very high pressures or high side a/c valves and tractor trailer tire valves among others. A/C valves are not installed into a rubberized stem but into a metal housing the threads of which are larger and far more substantial than your everyday automobile valve stem.

 

[SDeemer]

I'm skeptical on both counts. Here are two valve caps:

View attachment 10641​

In my hand, I can't feel a difference in weight between the two.

I just figured out why I couldn't feel a difference in weight: the "metal" cap on the right is actually chrome-plated plastic.

 

[JesusLover]

I too am a certified tech but only have 44 years under my belt.
A stem cap's main purpose is not to act as a backup in case of valve core failure and in the case of the plastic ones that don't have a rubber O-ring in side, they can't seal against a leak and are simply used to keep dirt from entering into the valve core and causing an eventual leak.
We don't have to change anyone's mind here. Everyone can provide their opinion and live within what they are comfortable with.
The OP was excellent in bringing to the forefront a problem with many of the metal caps and I hope people that have read through this thread, regularly check those metal caps (like when they check tire pressure monthly) because once they are seized on, it is not a good situation.

Techy, and others reading this,
Opinions and beliefs about everything, will truly and only be believed, by others, with some thorough investigation. But then some do not want to waist their time on what they believe is a trivial item. But is this thread that Trivial?
Question: Do Metal valve stems caps create issue with tire valve stems?
Answer:
Another Ref: https://www.bluestar.com/get_informed/article/tire-valve-stem-caps-do-your-tires-need-them
Quote:
Metal, and some higher quality hard-plastic valve stem caps, often have a rubber washer or seal inside to help make an airtight seal. This type of cap protects from dirt and moisture and also helps prevent air from escaping from a slightly leaking Schrader valve. In addition, the rubber washer or seal prevents the cap from loosening and falling off due to vibrations by acting as a cushion between the cap and the valve stem. Most caps, however, are a softer plastic designed for protection only and are not equipped with a separate seal.

True metal caps can corrode if left unattended or maintained properly. But isn't that true of tire maintenance in general? If a person doesn't check their tire pressures, unless they see a near flat or flat, then have they really performed the correct/ proper tire maintenance to promote tire life and safe operation, to prevent a crash and possible injuries or loss of lives.
Just ask yourselves, when was the last time I checked my tire pressures or had them checked. Discount Tire in AZ, and also operates in 34 other states, will check your tire pressure and ad air if needed: But people have to take the time to stop and let them do it! Is it really that important? The answer is up to each person reading this!
Have a Blessed day and a safe trip!

 

[JesusLover]

Another point that I just thought of: How many crashes, swerving to miss, or avoid a person or another vehicle, were actually caused by low tire pressures? Crash investigators do not check tire pressures! Low tire pressure do effect and affect vehicle handling characteristics! If investigators would checking people's tires involved in a crash, and find that they are not at proper pressure, shouldn't they deem the person "Negligent" and at fault in causing the crash?
Ask yourself: Would I want to have to swerve to avoid a crash, and then cause, because of a tire's or tires' low air pressure, what I was trying to avoid? Check tire before each short, or long trip, or at least weekly, and cheap. plastic caps may not be an issue!

 

[atc98092]

Discount Tire in AZ, and also operates in 34 other states, will check your tire pressure and ad air if needed:

Here in the northwest we also have Les Schwab, with locations in 13 states, as far east as Minnesota. Bottom line is there are tire chains all over North America that will likely check air pressure for free. But you're right, people need to make the effort to do it. I have a compressor in my garage, but that's not something most homes have.

 

[Dovidan]

Here in the northwest we also have Les Schwab, with locations in 13 states, as far east as Minnesota. Bottom line is there are tire chains all over North America that will likely check air pressure for free. But you're right, people need to make the effort to do it. I have a compressor in my garage, but that's not something most homes have.

Agreed!
Obviously easiest to have someone else do pressure checks & adjust as needed. A compressor is nice but given that most tires rarely need more than 2-6 lbs added a good ol' fashion hand pump works well with the added benefit of a brief upper body workout. 💪

 

[Flying Turtle]

For the longest time I've carried a little foot pump in my cars. Not bad for adding a few pounds. A couple months ago I traded it for a rechargeable electric that Costco had on sale.

Geoff

 

[dare2be]

I've neglected this thread. I took the car to a few places and only one of the caps could be removed by hand tools. I bit the bullet and had the other 3 tire stems completely replaced, at a cost of about $25 each. Using plastic caps now instead of the metal ones that came from the dealer.