Valve stems, cores, and caps "Oh My", and how tight is tight enough?

Yes, some rubber valve stems have a metal center and some valves are all metal except for a rubber gasket. The metal part of valves is almost always brass. Sometimes Nickle plated to look like chrome or to match aluminum wheels.

The two valves on the left are "Snap-In" rubber valves.  The two on the right are "Bolt-in" metal stems. By "Snap-In" we mean the valve is installed into the hole in the wheel by pulling on the threaded part of the brass until the small rubber ridge "snaps" through the hole.

The best way to know for sure is to look for a nut that "bolts" the stem to the wheel.  I would suggest a TR416 or similar as seen HERE from Auto Zone.  O'Riley's parts stores have a similar short stem.  You should be able to find similar in almost any auto parts store. These metal stems come in many lengths from less than an inch to 2" or longer (different lengths have different TR part numbers).  The hole in your passenger, trailer or light truck wheel is most likely 7/16"  Old VW wheels were 5/8" All 19.5 and 22.5 wheels should have come with a metal bolt in valves but those use the 5/8" rubber grommet/O-ring. Many metal stems sold at retail, come with two different rubber gaskets, one for each size hole. The gasket is just a snug fit and should just push into the wheel hole.

Note the nut has a torque spec of  25 - 45 INCH Pounds so do not over tighten the nut. I have found that a regular 9/16" wrench is just fine and you do not need a big ratchet wrench to tighten the nut.

Keep the stem short to lower the chance of the TPMS being knocked off if you get near a curb. There are some unique wheels that may require a bit longer stem to allow you to attach your TPM sensor. I suggest you have the sensors available when you install the bolt in stems to confirm sufficient clearance.

The main reason for metal stems when running TPMS is to prevent vibration of the stem which can fatigue the rubber stem.

While you are at the auto parts store be sure you have METAL valve caps. Plastic caps are IMO only good for keeping dirt and small birds out of the valve core area. Metal caps should have rubber "O" rings in them and can retain air if you are not running TPMS. Look in the thread end and you should see the gasket.

Each Fall, when I remove my TPMS for the Winter, I place metal caps on my stems. I will admit that one year I didn't do that and the valve core had a very slow leak but I ended up with a tire being damaged because it lost air over the 7 months between when I parked and when I was getting ready to go traveling.
  
I have a couple of posts that focuses on the valve cores. One on why they leak.

One detail is how to know how tight is enough for your valve cores. Over-tight can cause the small gasket to deform and even split and under-tight will result in a slow leak. After 40 years of installing valve cores I consider my fingers to be close to "calibration" but it would be better if you followed a specific procedure.

I did a test that may help. The spec for valve core torque is  1.5 to 5.0-inch pounds MAX  but I don't expect you to run out and buy a special inch-pound torque wrench as seen here.

To help you I devised this test. Using the test fixture I made when running my TPMS comparison I loosened a core till it leaked as seen here.

 Then using my torque wrench I tightened the core till the leak just stopped. I then continued to tighten the core till I reached about 1.5 Inch Pounds (this was 1/4 turn after the leak stopped) I then continued to tighten the core till I reached 5-inch pounds (This was 3/4 turn after the leak stopped)

  So I would suggest that you can simply tighten a core till the leak stops then rotate 1/2 turn more.

Here are sample core tools.

The one on the left is a "professional" tool but I have also used my home made core tool for many years. This is just an old scrap rubber valve stem with a cap that has the cut-out to fit a core.

I hope this helps you understand a bit more about valves and valve cores.


##RVT889

Do you have to replace valve stems when installing TPM sensors?

Got this question on an RV forum:
"I understand from the thread that you should use metal tire stems with TPMS caps. The ends of the tire stems on our trailer are metal with the only visible rubber part right where they go through the wheel. I am guessing these are still considered rubber stems and should be replaced prior to installing TPMS?"

"Metal" stems can be a bit misleading as some newer stems may have some brass showing. I posted pictures on THIS post showing standard passenger rubber valve, a "bolt-in" metal valve, and a new style rubber/brass valve.

When it is recommended that "metal" stems be used, what is actually meant is "bolt-in". You will see the nut that retains the bolt-in stem on the outside of the wheel for most of these stems.

The concern is that over time (months or maybe years) the extra weight of TPM external sensors may cause some vibration and movement of the rubber stem body which might result is a failure of the rubber portion of the stem.

I am not aware of any testing done on the new style rubber/brass stems with a TPM sensor screwed on, so I and others are erring on the side of caution when we recommend "bolt-in" metal stems.

Cracking and failure of the rubber part of valve stems is another time & temperature aging thing, just as it is with your tires. You visually inspect your tires monthly, as outlined in your RV  owner's manual, so just include the rubber part of your valves and just as you would replace your tires when signs of significant signs or aging (cracks) are found do the same with your valves. 

You could consider running your current valves until you get new tires and at that point have the bolt in valves installed. In the meantime, I would take a close look at your stems when doing your monthly visual inspection. You can push sideways a bit on the rubber/brass stem and look for any cracks. If you find any, that would mean you need to replace them sooner rather than later.

"Care and feeding" of your valve stems

I suggest that if you are looking for long "bent" metal stems you ONLY get them installed by a Truck Tire store. Preferably not just a "dealer," as anyone can sell tires, but a "company store" that is owned by a tire company or a store that is part of a large chain, as they are more likely to have a selection and actual training on proper installation of long truck valve stems. The shop should have the proper tool for bending the long brass stems without cracking them, if bending is needed.

With long stems it is also important to remember to not just press the air chuck or pressure gauge onto the end when adding air or checking pressure as you can generate a lot of force on the joint between valve and wheel. Always support the stem or hose extension with your other hand even if the stem or hose has a hard mounting, as you can loosen the mounting point too.

There are specifications for torque of the metal nut for bolt-in valve stems. (25 to 45 inch pounds) This is especially critical on your car or truck if it came from the factory with an internal Tire Pressure Monitoring System (TPMS). Many of the internal TPMS are made of aluminum for light weight and as such have very low torque specs. It is easy to break the aluminum nut or, even worse, the stem itself – which could cost you $50 to $100 to replace.

"Tire Review", a trade magazine for tire dealers, had an article on TPMS sensors and they point out the following:

"What is the torque value required for the nut?
Typical torque values for the base nuts on a TPMS valve stem range from as low as 35 in.-lbs. of torque to as much as 80 in.-lbs. of torque. That’s quite a range. This doesn’t mean that any torque value within this range is acceptable. It means that the torque specifications for the base nut on one vehicle might re­quire 44 in.-lbs., another might re­quire exactly 62 in.-lbs., yet another might specify exactly 71 in.-lbs., and so on. Don’t guess. Look up the torque specifications for the vehicle you’re servicing to make sure you use the correct torque.

Why should the nut be replaced every time a sensor is serviced?
The nut is made of a softer metal than the stem, so it will be damaged – not the sensor – if it’s over-tightened. The material of choice is typically aluminum. If the nut is over-tightened, it will develop hairline cracks."

NOTE: Those specs are INCH-Pound, not your normal Foot-Pounds. Here is a picture of my TPMS Inch-pound Torque Wrench.

Standard "metal bolt-in valves" also have specs for the nuts and those valves are usually brass or plated with nickle or chrome. I am not aware of any stainless steel valve stems for regular automotive use. There are some aluminum bolt-in stems too, but those are expensive lightweight units made for race car application which would not normally be sold without being identified as such.

Even valve core have a spec (2 to 5 in-lb) as there is a tiny gasket that can be distorted and even broken if you over-tighten the core. There are some special tools. But rather than buy some special tools I suggest you tighten core till air stops, add no more than 1/4 turn more, then confirm no air leak by testing with soapy water. When no bubble forms the core is tight enough. I then attach the metal valve cap to ensure no air is leaking. There have been a few cases of slow leak through the valve core that ended up as a tire failure as no metal cap was used. The cap is primarily intended to keep dirt out of the core area but is also a "backup" on preventing air lost past the core.

Whenever "messing" with your valve it's always a good idea to confirm there are no leaks with a quick spray of soapy water.

##RVT801

"Only" drove 750 miles with companion dual tire low on air

Quote:

Originally Posted by Charlie What should I do? I had checked tire pressure the day before and only drove about 750 miles when the right rear inside duel blew resulting in damage to the MH and the tow. Only the side wall blew and the tire stayed on the rim. This is the first time in over 25 years of RVing that I have ever had tire trouble. I only had about 14,000 miles on these tires that are less than 2 years old. I bought the best tires they recommended. I will not say the brand but it begins with M. I had pressure set at 120 psi and they were filled when the tires were cold and had not been driven for over a month, Should I be concerned about the other tires?

Should you be concerned? It depends. Why did the tire fail? If the failure was a sidewall flex failure (sometimes called a "zipper") from running low then there was most likely an active leak, i.e. puncture or leaking valve core would be on the top of my list. In this case the other tires are no more likely to fail next week than they were last week with one exception to be covered in a moment.

If you take the failed tire to a heavy truck tire dealer for the brand involved they should be able to confirm the mode of failure.

Since you were not running a TPMS (tire pressure monitoring system), all we know is that probably sometime between checking the tire pressure and 750 miles later (2 days?) one tire had lost most/all of its air. We also know that the outer dual was run with possibly 100% overload so it probably sustained internal structural damage that shortened its life (months or years). Since we do not know how many miles at what % overload, it is impossible to predict -- so the suggested best practice is to replace the companion dual.

One thing we can do is to use this as a learning experience. With a TPMS a driver would get early warning and many times can stop before a tire is damaged and, by extension, avoid damage to the RV and even not damage the mate in a set of duals. A single warning in the life of a TPMS (years) could save much more than the cost of the system.

Now as to the other possible reason for a tire to lose air. It is possible for a piece of grit to get into the valve core and allow air to leak. I suggest you review the posts on "Valves" (list to the left) and you can see an actual example of a leaking tire and the grit that caused it. So, as I have pointed out in the past, the very act of checking air pressure can sometimes result in a leak and potentially a failed tire.

##RVT797

What valve should you use?

We have discussed valves previously but this time I want to give you some facts and numbers to help you buy the correct valve for your application.

Basically there are two criteria you have to get right. The size hole in the wheel and the cold pressure spec for the tire inflation.

For passenger and light truck wheels that use the standard "snap-in" rubber valves, you will usually find them to be either 0.445 to 0.461" or 0.618 to 0.633" dia hole. There is also a maximum metal thickness of 0.156" at the hole. Some aluminum wheels have special step machining to cut the thickness down to the proper dimension. Most steel wheels do not have this problem as they are thinner than 0.156" and run closer to 0.070". These "snap-in" have a 65 psi max spec and carry part numbers such as TR412, 413, 414, 418, 423 and the large dia. TR415 & 425.  The difference is the total length which runs from 0.88 to 2.00 outside the rim surface.

Note. some have chrome covers but are still basically the same rubber valve under the thin cover. Do not be mislead into thinking these chrome valves are like the bolt in metal valves. Look for the TR number.

 The picture to the right comes from AllTireSupply
and you can order valves from them.
 I would never use any of these rubber valves if
 I have a TPMS or on any RV.

The next group of valves are bolt-in metal and are rated for 200 psi. Now these are designed to fit the same wheel hold dimensions as the above passenger & light truck wheels. Some of these will come with two different size grommets so you can fit either diameter hole. Just be sure you get the correct grommet.




These carry the P/N TR416 or TR416s for the small dia hole depending on which size wheel hole and these are about 1.4" long. This picture comes from MeyersTireSupply. They are a wholesale company in Akron, OH so you may need to get the name of a dealer in your area from the Meyers web site. They also have a 2" long TR416L. The nut torque on this type valve is 25 - 45 in-lb

There are also special High Pressure snap in valves rated for 80 or 100 psi cold set pressure as this one also from Alltire Supply

The 80 psi valves carry the P/N 600HP & 601HP at 1.2" & 2" long

 The 100 psi 801HP & 802HP are 1.3 and 2: long

You will probably find these on new larger pickups .

 Now we move to the big boys for larger "Truck/Bus" applications which for the RV owner means 17.5, 19.5 and 22.5 diameter wheels. There are some that are made especially for aluminum truck wheels but the standard bolt in valves are rated for 200 psi. These fit a hole dia of 0.618 to 0.633". These come in a number of lengths both straight and bent to 90°. Their P/N are TR500, 501, 570, 571, 572, 573, 574, 575. If bent there is a "c" suffix. The nut on these should be tight to 35-55 in-lbs

Your application will probably depend more on your wheels that the selection for small trailers and other vehicles with 16" or smaller dia wheels. When you discuss buying valves you should have your wheel information available.

Now remember if you have aluminum wheels you may need special valves. The valves should use tire mounting lube on the grommets when installing. You should replace the rubber valves or rubber grommets whenever you change tires. I would squirt each valve with Windex or some spray cleaner and confirm it does not wiggle in the hole at least once or twice a year to ensure the nut is not loose and the grommet is still sealing properly.


Bottom Line
Valves are only a couple bucks each so it is false economy to not replace them every time a tire is dismounted. Always use metal caps or TPMS sensors on the end of your valve stems to keep dirt of the core. If you have a lot of dirt or mud on the valve wash it off before removing the cap or TPMS..

Long Term Parking - Winterizing

Now is the time many RV owners are "winterizing" their RV. Even if you are in Arizona, you might be getting it ready to be parked for many weeks or months. There are a few things you need to do to help preserve your tires.

1. When you wash your RV prior to storage be sure to clean the tires. The easiest thing to do is to treat your tires just as you would the side of your RV. Wash the tires with the same soap & water you use on the RV body. You wouldn't use SOS pad on the bodywork so don't use coarse scrubbing material on the tire.

2. Inflate to the pressure shown on the tire sidewall. This will decrease the tendency to flat-spot and make the tire flat on one side.

When I was checking the inflation I discovered one tire was almost 30 psi low. I knew the tire had not lost air when it was being driven so I immediately suspected that when I removed my external TPMS sensor the valve core must not have properly seated. This was confirmed with a shot of household cleaner. Here you can see the small bubbles that confirmed the 3.5 psi per week air loss past the valve.

3. If you are not parking on a concrete floor or pad it is suggested you not park on asphalt as the oils in the tar can attack the tread rubber. It is also suggested that you not park on dirt or sand as the moisture can migrate into the tire and possibly cause corrosion of the steel.

I have some pressure-treated boards that are large enough to completely support the contact footprint.


Here you can see the board and the reference footprint for a front tire.








You always need to completely support the entire footprint. Both in length and width. These pictures show what NOT TO DO.
                                                                                Too narrow










Off center



                                                                                             Just Right











 Be sure the support is wide enough for both duals.









Finally, be sure to cover the tires to protect them from direct sunlight, which can cause UV damage and overheat the tires.

If you haven't read my series on Tire Covers simply check "Tire Covers" on the label list to the left.

A little bit of preventive care can help avoid future problems and extend the life of your tires.


P.S. Don't forget that even when parked you should check the air pressure once a month. If I hadn't checked the air in the tire with the leaking valve it probably would have been flat by next spring and might even have been damaged and unsuitable for highway use.

Valve extensions

A review of some of the various RV forums will reveal that a fair portion of people have had some form of problems with valves and valve extensions. One poster provided a nice option that worked for him.

Jake L. from South Carolina had problems with getting his pressure gauge and inflation chuck onto his valve stem through the openings in his rim & hubcap.

Jake had some 135 degree stems installed but the company doing the work apparently did not do the work correctly and his new stems leaked. He now has regular straight stems that don't leak but he can't get the double foot chuck to work.
His solution was to use short extensions some call "Alligator". Here is a picture of the short extender.

Note the nice metal valve cap. Some people incorrectly believe that the "Alligator" cap is an acceptable alternative to a regular cap as it allows you inflate or check the air pressure through a small "trap door". The problem with using the cap in this manner is that it will allow dirt and grit to enter the valve stem chamber.           

I covered the topic of dirt in the valve core 11/2/12. Check it out if you haven't already read it..


Here you can see that this short extension solved Jake's problems. 

Regarding the issue of keeping dirt and grit out of the valve core chamber, I think this is something very few ever think about.

 My short extension even carries the brand name "Alligator.

 This is what the end of the Alligator extension looks like.

Here you can see how the extension works.


This part should not be considered a cap but just a very short valve extension.

It would be very easy for the end of the Alligator cap/extension to collect dirt which would be blown into the valve core area so if you use an "alligator" short extension be sure to use a cap or screw on TPM sensor

Why do tire valves leak?

Many people who experience a tire blowout insist they had checked their tire pressure and that their gauge was accurate. So they blame the failure on a defective tire. However, what could have been the culprit was a bad cap on their valve.

Now I must say that if you have a TPM sensor that is basically a screw on valve cap, this warning probably does not apply as long as you ensure the valve stem is not dirty or covered in mud when you remove or install the TPM sensor.

A good valve cap is metal and has a small gasket or O-ring in it to seal against the end of the valve stem. The cap serves two functions. Primary is to keep dirt out. Second is to be a backup to keeping the air in if the valve core develops a leak. A cheap plastic cap may work on a 30psi passenger tire but I doubt it will last too long on a hot high pressure Class-A TBR tire.

Lets take a close look at the valve core.

I have labeled the plunger that opens the valve to let air in or out "P". The gasket that seals the core inside the valve stem "S". Note the small indentation that indicates this core has been used but not over tightened.

Finally the location that opens when you press on the plunger "V" is a small circular opening.

To the right is a graphic from Wikipedia showing how a Schrader valve operates.

If you look closely you can see the valve opening letting the air out.

Now lets look at what can happen if you get a single piece of grit stuck in the valve area.

I included the head of a straight pin so you can see just how small that bit of dirt is.

Now lets see what happens if this valve core with the grit in the valve is used on a tire.

Now you see why using a good valve cap is important. You must keep the dirt out of the valve area. If you discover a leak as shown in the picture above, cranking down on the core will only damage the core seal (the black band in the pictures above) and will do nothing to stop the leak. It is best to simply replace the core with a new one.

Why do tires fail?

Simple question but as with almost every question about tires, the answer is not a one liner. Stick with this post. It's not short but it really isn't technical and I'm sure every reader will understand the concepts.

When looking at why tires fail we need to first exclude the obvious damage caused by external objects i.e. pot holes, curbs, chunks of metal, glass or rock or other trash and junk on the road. Second we'll exclude broken valve bodies, leaky valve cores, valve gaskets, extension hoses, and cracked rims.

What's left will be a structural failure which would almost 100 percent of the time will be a detachment of different parts or components of a tire one from the other.

Most tires are made up of 20 to 30 different components such as different steels (belts and bead are not the same steel) textiles such as Nylon, Polyester, Rayon, Aramid. Then there are the various different rubber components such as Tread, Sidewall, Innerliner, Steel skim, Wedge, Flippers, Chaffer, base tread, Inserts, and other bits and pieces.


Each component is selected for different reasons and contributes both advantages and disadvantages to the total. Each component must "stick" to its neighbors both in the un-cured and cured state. The interface between two different components is weaker than the individual components but it must hold together through millions of cycles over a 200 degree temperature range.

All would be just fine if a tire were made completely of inorganic materials such as metals, stone or even ceramics. There are numerous formulas for the strength and fatigue limits for these inorganic materials.

The issue with organics (wood, rubber or other materials made from oil such as plastics) is that their strength has a "T" or time function. If you build a bridge of stone, you can calculate the maximum load it can sustain and as long as the structure isn’t changed due to external damage its strength will be the same the day it’s built and 50 years later. If I build a pressure vessel of steel and put 150 psi in it and it doesn’t fail I would have every expectation for it to continue to hold that pressure for decades, again excluding external damage.

However, if I build a pressure vessel of organic materials (a tire) it might hold 150 psi the first day or maybe the first few days but at some point it can fail. This principle is not something many engineers think of today because they don’t design bridges of wood but 100 or 150 years ago when wood was common they learned that a bridge that was strong enough to hold a railroad train to drive across, it could fail if the train parked on the bridge.

I educated some fellow tire engineers about this “T” function when I proved, through lab experiments that it was possible to fail a tire with high pressure above its stated max 18 days after it was initially inflated.

The other condition that affects and changes the “T” in the equation is temperature. Organics experience constant change (loss) in properties as the temperature increases. The rate of change (aging) doubles about every 20 degrees of increase in temperature, so it's not easy to calculate or predict the time it will take for an organic structure to fail unless you can control the temperature over time.

Bottom line. It’s a combination of temperature (heat) and time that causes tires to fail. A tire that spends its life in Flagstaff, Ariz., could last twice as long as a tire that spent its life in Phoenix if all other operating conditions were identical.

As the owner of an RV you can significantly affect one factor and that is the heat generated internal to the tire. When you run fast or overloaded or under-inflated you are running hotter. This means you are speeding up the rate of "aging" of your tires and can expect to see a tire fail before it wears out.

Quick post on rubber valves

I continue to see posts from RV owners saying they have "Rubber" valves. This even though most rubber valves are only rated for 65 psi cold. There are some rubber valves rated for 80 and even some rated for 100 psi but these are not interchangeable.

How can you tell if you have the correct rubber valve for your application without dismounting the tires?

A quick examination should give you an idea of what you have.


What to look for

First unscrew the cap. See if the the only metal you see is the threaded part right under the cap. This is just over 3/8" long.


This valve is usually about 1-1/4 long outside the wheel. Is designed for a hole in the wheel of 0.453 and is rated at 65 PSI Max Cold inflation.


If you see metal even with the cap on like this

It is either a 600HP series LIKE THIS which is rated for 80 psi Max Cold inflation or a 801HP series rated for 100psi Maximum Cold inflation.


NOTE these are NOT interchangeable as the 600 is designed for a rim hole of 0.453" while the 801 needs a hole diameter of 0.625".

Now even if your cold tire pressure does not exceed the rated capacity for the valve you have I strongly suggest you consider switching to a bolt in metal valve with the appropriate rim hole size as if you run valve extenders or hoses or external TPMS you are probably applying more side load to the valve that it was initially designed to accept.

Also you should be running metal valve caps not the cheap plastic ones that probably were OE for if the valve core leaks due to a bit of dirt the metal cap can hold much more pressure than the plastic one.


NOTE if still in doubt you should have the valves inspected by a tire dealer. Call and ask if they have a Technician ASE Certified on tire inspection. If not, select another dealer.

Valve placement

Quick post to answer George's question
"Valve extensions for inner dually tires
The awkward placement of valve on outer rear dual tires: why do they face inward and do they HAVE to be that way."

If you look at the valve placement, the "inside" of your outer dual is really the "outside of the wheel if that wheel was on the front or was the inside dual. This means all wheels can be the same. If the valve was on the outside of the outside dual you would need a different spare tire/wheel assembly as you can't have the valve on the inside of your fronts or inside of the inner dual and clear the brakes.

Tire Valves - Not just those little rubber things

I gotta start off by telling you something my wonderful wife Nancy says bout me. If you ask me the time of day, I may end up trying to tell you how to build a watch. I've decided I will try to start some of my posts with a one paragraph summary. If you want to know more then you can read on, but you have been warned.

90+% of RVs should have bolt-in metal valves and it won't hurt if we used them even on a Tear-Drop trailer. Rubber valves on your car should be replaced whenever you get a new set of tires. The rubber gasket part of metal bolt-in valves should be replaced whenever you get new tires. If the valve core is leaking, replace it.

OK now for those that want the details.

Recently a friend, Nick Russell, the editor of Gypsy Journal had a tire failure.

This was an inner dual and you can see right through the tire sidewall where a big chunk is missing. While some would blame the tire and say it was defective and that he had a "Blow-Out". Nick is a bit smarter than that. He knew he had been having problems with air leaking out but there was no puncture. The "Root Cause" of this failure was traced to the use of a rubber valve on his Class-A size tire. The valve stem did not seal properly and he had a slow leak. The end result of someone trying to save a couple of bucks cost Nick over $700 for the service call and new tire.

For those of you wondering, we will cover in future posts a number of specific types of tire failure each of which leave their unique tell-tale signature

Standard rubber valves like the T-414 series are rated for a MAX of 65 psi and for use on the relatively thin passenger rims. There are rubber valves such as the 600HP rated for a MAX of 100 psi but neither of these "snap-in" rubber valves belong on an RV with the possible exception of some very samll trailers and some Class-B units that use standard passenger tires.

Class-A, Class C and most trailers have inflation pressures that exceed 65psi with many above 100psi so a bolt-in metal valve is the only one to use. It is important that the tech doing the installation of these bolt-in valves apply the proper torque. Small bolt in valves such as TR-430 use 25- 45 inch-pounds of torque.



The majority of the TR-500 series use 80-125 inch-pounds.

If you discover the valve core is leaking don't just crank it tighter like you would a leaky water faucet. All the core needs is finger tight. 1.5 to 5.0 inch pounds MAX. If you over-tighten the core, you may split the core gasket (black in the graphic) and it will just leak more. If you look at the graphic from Schrader you will see the part that that lets the air in and out can't be tightened. Your tire dealer should be willing to give you a new valve core for free. You should ALWAYS use some type of cap with metal the best. The primary purpose of the cap is to keep dirt out but a good metal cap with internal gasket can keep most of the air in too.

Watch THIS little graphic on how a valve core works.


A final bit of warning. On your car you may have a Tire Pressure Monitor System. Most of these are Aluminum not Brass so they need special stainless steel valve core and they may be bolt in and have low torque requirements. If you need to service the OE TPMS valve you need to go to a car or tire dealer as they have the correct tools. I will be covering TPMS as a separate topic in the future.