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Bad Valve Stems / CO2 Inflator
This season I’ve been having tire issues. More accurately, valve stem issues. I check my tires daily when on the road and before each trip. About 6 weeks ago I started having problems with the valve stem on one of the rear wheels (315’s). When I removed the valve stem cap, air was leaking out. I couild depress the stem a couple of times and usually get it to stop. I finally had to call a mobile tire service to come out and replace one of my valve stem cores.
Now, 6 weeks later I’m having similar issues on the front wheels (365’s). These are normally inflated to 125psi per Marathon’s recommendation, and is the maximum pressure indicated on the tire itself. Before my trip the other day, the left fron wheel was down to 70 lbs after having been parked for 10 days in Creede, Colorado. Worse yet, when I removed the valve cap, I could hear air hissing. Again, I vigorously pressed on the valve tip a few times and the leakage stopped. Houston, we have a problem.
I used the bus air to get the wheel back up to 110 lbs. 110 wasn’t great, but sufficient to get us to the next air compressor. We drove about 75 miles to Alamosa before I finally found a tire store which could help. I stopped a couple of times along the way to make sure my tires weren’t getting hot and fortunately, they stayed cool, under 110 degress F. I also limited my speed to about 60 mph along this route, constantly worring about the front tires. I hate having to constantly monitor a problem while driving….
The tire shop in Alamosa had better air pressure, however, they still couldn’t get 125 psi into my 365’s. We were able to get 120 psi, however, the tires were already warm and so it was still less than ideal. While I was there, I had the guys take a look at my valve stem cores. When the first core came out, the problem was immediately apparent. The core, a plain brass model, was corroded. Evidently, this corosion was affecting the stem seal and thus leakage was inevitable.
I managed to get a couple of new stems installed in the front tires and the tire mechanics informed me that the “red ones” were for passenger cars wheras the “black ones” were used for trucks and had a higher rating.
From what I could see, another major difference was that the black ones were plated and logically less likely to corrode than plain brass.
Later, I researched valve stem core color codes and got different information. Apparently, the red cores are rated for 250 degress F and the black ones 225. Both are rated for 200 psi. The tire guys were technically wrong, but the new stems seemed to be OK. Later, I found that there is a third color, white, which is specified for aircraft tires and is rated for 500psi.
We weren’t able to change any of the rear wheel valve stems, nor do we know why the brass ones are deteriorating. The tag axle stem had some kind of very long core of a different design, and oddly, when it was removed the tire lost no air at all. It must have an inner valve below the outside one. Must investigate. On the duals, we couild not change the stems without removing the wheels, which we opted not to attempt at this facility. Fortunately, all six of the rear wheels have been generally OK and not leaking, so we took off satisfied. They guys at the tire shop gave me enough black stem cores to finish the job later, and then didn’t ask me for any money. I gave them a nice tip and headed out to Colorado Springs, about 160 miles away.
The trip to Colorado Springs was uneventful. A couple of stops and temperature measurements confirmed that everything was ok.
The next morning I checked the cold tires and both front wheels were in the 110 psi range. So, how do you get accurate air pressure into your cold tires when you have to drive to a truck stop or some other heavy duty location to get air? This isn’t a new problem but it is one for which I’m totally fed up. I decided to look into a portable tire inflation system.
Last year I read a post by another Prevost owner who was recommending the PowerTank solution. PowerTank is a portable CO2 based system that provides good pressure for topping off. Their system run in the $500 to $600 range depending on the options you choose. They offer a 10lb and a 15 lb (pounds of CO2) system. Since all I really needed was the tank and regulator, I deciced to see if I could build one myself. Below is the system I put together, for a total cost of about $185.
I bought the tank, full of 20 lbs of liquid CO2 from an industrial gas supplier for $110 and a used regulator, called a “nitrogen purge regulator” for $50, plus an adaptor for it to fit the CO2 flange, and a quick disconnect chuck from Lowes. The tank can produce as much as 800 PSI and I opened up the regulator to put about 160 into the air hose. Both tires needed about 10 psi to top off and this took about 60 seconds for each one. CO2 gets pretty cold and you can see some frost on the regulator, but it wasn’t a problem. The flow rate was good and even while filling the output pressure gauge stayed fast at 160psi. Success!
For transport and storage, I remove the regulator and tank adaptor for safety. The 20lb CO2 tank is fairly easy to handle and safe to store anywhere under the bus.
I’m really happy with this solution and never again do I have to search for a truck stop for filling my warm tires. Sometime this winter I will have all the stems replaced and may install an internal (inside wheel) TPMS.
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37 Replies
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Good grief Fred, 125 psi on 365’s is the correct pressure for a weight of 10,500 single. Is your front end in the 21,000 lb range?
Have you had Equal in those tires with the shrader problem?
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Fred, if my mouth looks open, it is because it is.
If you have Equal in the tires that would explain your constant leakage issue. If not (and even if you do) you need to find out why and how you are getting moisture in the tires. The trucks stops that fill your tires must never drain their compressor tanks.
But I want to echo times reaction. You only inflate your tires based on your axle (or individual wheel) weights. Marathon either knows you have 20,000 pounds on that steer axle or they are giving you really bad advice. But apart from pressures likely being wrong you may have a problem with Equal being in a tire and the wrong valve cores instead of the cores with the screen mesh filter, or you have a problem due to moisture and corrosion playing a part in the issue.
You may have to break down the tires to determine what you are dealing with.
My final free advice which is worth every cent you pay for it is to put a quick connect air fitting on your aux air system and fill your own tires. Buy a good quality combination fill valve and pressure gauge along with a straight foot tire chuck and you can check and fill your tires from your coach air system when it is convenient for you. Then you don’t have to drag that potential bomb around with you.
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Jon,
Yes, as far as I know the tires have Equal in them, however this was done just a few days before I bought the coach. I have not added a great deal of air to any of the tires and have never fully depressurized any of them. Therefore, I don’t have any real knowlege of the moisture content, only the symptoms.
The Marathon advice is 125/120/90 psi. I have it on a sheet. I haven’t weighed the coach yet as it’s on my hope-to-do-soon list. Meanwhile, I’m running my tags at 115 PSI because I’ve since learned that once you reach the proper pressure for a given axle weight, higher pressure principally affects the smoothness of the ride. Tread wear isn’t an issue. By running 115, I have better margins in the event of a leak, and the tires will run cooler. Although I’m not yet certain, it seems that my tag axle may be slightly overloaded. I say this because the tag axle tires are always 10 to 15 degrees hotter than all the other tires, even with the higher pressure. When it’s time for tires, I may opt for 365’s for the tags. I’m also favoring the super single configuration for the drives and may look into it in about 5 years.
The screen mesh valve cores are a new bit of information for me. I will have to wait until I’m in a position to break the tires down to check into this. Where is the screen located? On the stem base, I’m thinking, not the valve core.
I may not have made it clear that the bus aux air system would not fully inflate the tires. The Aux air system cycles between 90 and 120 PSI. As soon as I chuck a tire into it, it starts dropping. Soon, it is below the desired pressure and when it drops to 90 PSI the compressor comes back on. If it drops to the tire’s current pressure, equalibrium happens and that’s the end of the exercise. It’s practically useless as a tire inflation source when the target pressure is 125. As I said before, the most I could fill a tire with it, with the engine running at high idle, was about 105-110 PSI. I had to drain the aux air system down to 90 to get it to jump back up to 120 and then try and steal a few pounds from it before it reached the current tire pressure and equalized.
I must object to the characterization that the CO2 tank is a bomb. It is almost exactly the same as a CO2 fire extinguisher which are by definition, safety equipment. They are in use everywhere (every soda fountain has one, for example). All things considered, I’d say that CO2 tanks were MUCH safer than a tank of propane, which few people seem to worry about. On my coach, the tank fits snugly in the driver’s side 3rd compartment, where there is nothing of any note apart from sewer hoses and plastic storage boxes. It also stays within a reasonable temperature as well as there are no heat sources nearby.
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If you have Equal in the tires you need a special valve core. Google “equal valve core” for pictures. The regular valve cores will leak again after you check the tire pressure a few times. The equal gets on the valve core seat when the pressure is released and prevents them from sealing. Those are very high tire pressures!
Bob
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Fred,
In order, the question about the valve cores was answered correctly in the previous post.
The information about tire pressures seems off the charts and you do need to weigh the coach. Although you are significantly better off with more pressure than needed. I would guess if you have 365 on the front you are probably in the 100 to 105 PSI range, the drives I’m guessing 85 to 90, and if I surmise correctly you have 315 on the tag probably around 90.
If you have much more than the weight I am guessing on the tag then your steer axle pressures will be lower and the tag pressure higher along with the drive pressures. That’s all a guess and the weight will determine if I am right or if Marathon is right.
Your aux pressure for filling tires is the 120 the coach with the engine running provides. The aux compressor is just for the house requirements so if you need to fill tires, start the engine.
Unless a tank under that pressure is secured, if it should become airborne, such as in an accident or sudden stop and knock the top valve or pressure regulator off maybe “bomb” is an overstatement, but I am pretty sure if that happens you will not be able to buy excitement such as a rapidly emptying CO tank can give.
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Fred, i’m with Jon on this one. We had the same problem 2 yrs ago after putting drives and tags on because I assumed (makes an ass out of you and me) that as long as they were putting Equal in the tires, they would use the right valves. It won’t happen again….I stand and watch the entire process. Why would anyone carry CO2 when you have nice dry air right from your compressor and all you have to carry is an air hose ?
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With all due respect….Marathon is not in the tire and wheel business
125 psi in 365s, is 20 psi over inflated on steer axle.
Please go to the Michelin tire charts after you weigh your bus. Most truck stops have an accurate scale and reasonable cost around $100 for the weigh, takes less then 5 minutes on the scale.
Owning a Marathon for over 5 years and reading service bulletins and attending Prevost and Marathon tech seminars I have never heard either suggest 125psi in 365s.
Question…… did Prevost or Marathon believe you had 315s on your steer axle ?
I believe both Jon and Tom are trying to offer you excellant advice based on many years of Prevost bus experience.
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If Fred’s bus came with 315’s, 125 in the steer would be correct. If someone changed out the steer’s to 365’s, then that may explain the difference. I’m 17,500 on the steer Fred and was running 125 with 315’s and after changing to 365’s the chart called for 100. I set them at 105.
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Thanks to all for the helpful advice. I will get weighed as soon as possible and report back.
-fred
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Fred,
Serious question and not intended to cast any criticism on you. We have discussed the bulk of the contents of this thread over the years. The serious nature of tire pressures makes it a very important topic, and tire pressures are at best a guess unless the coach is weighed on each axle.
You have been around a long time. Where have we missed the boat in reaching members that need information like this imprinted in their brain? There are certain topics and pieces of information that are so important that every owner, regardless of skill level, mechanical understanding, or experience needs to know and apply to their coach. How can we grab everyone’s attention when we are discussing these items, especially those that have a profound impact on safety. We are not serving our members if these critical topics are not reaching them.
What do you do on your web site to make the critical posts and topics get to everyone?
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While we wait for Fred to answer your question, I’ll give it a shot.
It has to do with currency of the information. Even if I read it now it doesn’t really “sink in” until I need it and can apply it. In medicine is the concept of “see one, do one, teach one”. Until step two, I don’t really know what I am doing.
The same issues creep up all of the time on any site open to a large group of people. I see it all the time on a medical administration listserv I follow. How many times can you respond to a post that asks “what do YOU do when a doctor shows up drunk”?
Another thing that may help is the search function here. If someone titles their post inventively as I tend to try to do, or if they misspell a critical word, the search function that only looks at thread titles is of little use.
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this thread brought up some interesting topics for me.
i have seen bad vavle cores with brand new tires and vavle stems put on. valve cores just dont seat properly, providing you a nice slow leak. dealing with this now and bought a TPMS setup to monitor while i am driving. adds a little security, but still not providing a solution to the problem. once i am back i will be talking to the place that did my tires about the cheap vavle cores they installed.
on another note, i had a question about tire preasures and temps while driving.
what are people seeing for each tire while driving and what is acceptable? some tires seem to get hotter then others and see a larger increase in pressure from cold temps. specifically the inside drive tire.
where should i be concerned in terms of temps and pressure?
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First, while I understand what Karl is saying about how to retain information, tire pressures are so important we have often repeated it in almost every discussion about tires and pressures that as soon as a person gets a coach and loads it, the next step is to get it weighed.
We have beat on that drum over and over. Usually the thread is started by a new owner, but regardless we will repeat that advice regardless of who is engaged in the conversation. It is such a critical safety issue we are remiss if we don’t make the point. As to Karl’s observation, getting the coach weighed for purposes of knowing the correct pressures is not like learning a procedure or adding a skill. This is as fundamental as checking the oil level which I really hope owners are doing.
Charles is correct in his statement that even new tires, stems and valves can fail. The tire bead can leak, the valve stem can leak at the point where it enters the wheel, and the valve core can leak. That is why we always need to be aware of our tire pressures. Just to repeat and stress why this is important, our tires are irrepairably damaged if they are run at 20% less than the inflation pressures based on weight. They may not fail right away, but when they do fail it is likely to be a catastrophic “zipper” failure in which the entire tread separates from the tire suddenly. It is not uncommon for that type of failure to result in a handling issue, but it can result in expensive damage to the coach.
I get to know my tires. I once had a tire with a leak so small it took about a month to lose 5 PSI. Now my tires only require perhaps a pound or so after a month or two. If that changes I will be looking for the leak although small ones are almost impossible to find. I make a habit of doing a tire check before rolling out of the garage on both the bus and the toad.
As to tire temps, I have my tires inflated to the specified pressures plus 5. I had my gauges checked at a tire store to the store’s certified gauge. I still want that small extra margin. Running tires at those pressures have given me consistent temps if I get the IR gun on them as soon as I stop. I shoot at the center of the tread, and on 85 degree days, dry roads, I am expecting to see around 135. The tires on the sunny side of the coach might be a little higher than on the shady side, but my tire temps are usually very uniform. I have no idea what happens to my tire pressures as they heat, but the tire manufacturers know the pressures are going to rise so I don’t worry about hot pressures or tire temps as long as my cold pressures were OK. It is not the tire pressure or the tire temp that is important, but if one is way out of range of the others that is noteworthy. If
Charles has variations on his drives, inner to outer, my first reaction is if the cold temps were the same. My second thought would be if one of the tires had to be replaced and there is a small variation in tire diameter.I do occasionally shoot temps at the wheel close to the hub. The fancy hub caps make that difficult now, but what I am looking for is consistency like I do with temps. An especially hot wheel compared to all the others gets my attention because it could be a bearing issue due to lack of lube, a dragging brake, or an indication the hub nuts were overtightened.
Checking tire temps at a rest area is just a neat way to look for something out of sync with the other temps and that is usually a first indication of the problem. It gives me an opportunity to walk and stretch so there is a side benefit.
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Jon
I belong to a website for Ford trucks and they have a section at beginning of their forum of things everyone should do to their trucks. For example people with 6 liter diesels should do the following. So you could have a permanet thread that would have a list for things owners should check and do. This would be a short thread created by the admin that would always be at the top.
http://www.ford-trucks.com/forums/303583-6-0l-diesel-tech-folder.html
Speaking of top is there a way have a thread start with the news comments as opposed to starting with the original poster?
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Greg, when you open a thread you can click on a box that takes you to the first new post. I think it is “since last read”.
While I fully agree each owner has certain things that we all consider to be important things to do, all our priorities are different and so are our skills and available equipment. Some folks for example are not going to check their tire pressures because that is not what they are willing to do. Some won’t pump their own fuel. The bottom line is we likely will not be able to ever tell others what they should do. All we hope to do is make them aware of things they need to be aware of, or things beyond the limits.
I know it is important for people to not eat razor blades, but I don’t tell folks that because I assume they would somehow understand that.
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