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# Slow leak due to rims, can't find puncture

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## Slow leak due to rims, can't find puncture

(OP)
I have 14 year old mag wheels on my car which originally had tubed tyres but I moved to tubeless tyres recently.
Off late I am loosing 1psi / day in one of the tyres and 0.5psi/day in an other. I could not find a puncture. This number has risen over the last one year.
Is there a way apart from getting tubes I can diagnose and fix this problem?
Should I be worried that slow leak is becoming faster?

### RE: Slow leak due to rims, can't find puncture

How did you inspect for "punctures"?

Is the pressure loss while driving, or even just sitting ?

I expect 1/2 psi per day will create obvious vigorous bubbles if submerged in water, or sprayed carefully with soapy water.
http://img-aws.ehowcdn.com/640/cme/photography.pro...

Tire bead seats, tire valve stem seats, and tire valve cores all are responsible for an air-tight wheel/tire assembly

Who installed the tubeless tires? Details like cleaning old rubber AND corrosion off the rim bead seat AND tire valve seat are all important to prevent problems just like yours. It is not a 1 minute job, and takes some close visual inspection.
I've had to clean, sand and even use epoxy to smooth some badly corroded sealing areas on alloy wheels that were otherwise in very good condition.

In the last 6 months, tire valve seat problems have emerged on 2 professionally installed tires of our friends and family.
- The older car is a 2008, just 8 years old. One repair was on a tire that set off its low pressure indicator after months of service. The pro repair still showed a very fine trail of bubbles from the valve/rim joint when the stem was leaned outward, but 10X less than caused the mighty slow leak. I let that one go for now. Had to submerge that one in clean water, with good light.
- The other was low pressure alert and one soon-to-be flat tire the day after some new tires were installed on a 2012 Ford Flex with circus wheels by a very highly regarded large local indie shop. Soapy water revealed a Big leak around a (newly installed) tire valve.

### RE: Slow leak due to rims, can't find puncture

First I would suggest you do some diagnostic testing.

Try using soap bubbles to find the leak. I've immersed an assembly in a laundry tub, but I'll bet a kiddie pool would work.

Also, be aware that alloy wheels are somewhat porous. They use a clearcoat to seal the metal and sometimes that clearcoat deteriorates over time. At a half a psi a day, that's where I would look. And be aware that since the whole metal matrix is porous, individual bubbles might be hard to spot. The one I did had bubbles that would cling to the surface of the metal and when wiped off, took a half an hour to return.

### RE: Slow leak due to rims, can't find puncture

You have some small leaks somwhere. Put some "gunk" in the tire and all small leaks will be sealed. I have had no problems with using liquid sealants on several cars and trucks.

### RE: Slow leak due to rims, can't find puncture

Agree with CapriRacer that wheel porosity is quite possibly the culprit. When checking for this, the bubbles tend to be tiny, much smaller than what you'd get coming out a leaky valve stem or a puncture, so look closely. Been there, with pressure losses of 1 psi/day and higher. It is a bit odd to see what looks like solid metal letting the air leak out.

Norm

### RE: Slow leak due to rims, can't find puncture

Another possibility is that your aftermarket wheels don't have a tire bead friendly rim and don't follow an SAE bead contour.

### RE: Slow leak due to rims, can't find puncture

Looks like Elephant was in the room today. Sept 14

I wonder if his leaks are fixed.

### RE: Slow leak due to rims, can't find puncture

Cibachrome,

Just a minor correction: SAE doesn't specify rim contours or get involved in this area.

The folks that specify rim contours are the tire standardizing organizations, such as The Tire and Rim Association (US), the European Tyre and Rim Technical Organization (ETRTO), and the Japanese Automobile Tire Manufacturers Association (JATMA) and other similar groups. In the area of rim contours, all these groups coordinate with each other, so any rims manufactured to those standards are compatible world wide.

And just an FYI, I do not know of anyone who did not follow those standards - EVER. There have been some that were out of spec, but that was part of a batch that were mostly in spec. So I consider it extremely remote that non-standard rims are to blame for the OP's problem.

### RE: Slow leak due to rims, can't find puncture

1 psi loss from a 30 psi tire (assumption) is moving from 45 psia to 15 psia, so a tripling of volume.

Making some guesses: the tire interior volume is say 6 inch diameter on an 18 inch centerline for a volume of

(pi*6^2/4)*(pi*18) = 1600 cu inches => so the leak should see almost 5000 cubic inches/day or 3 cubic inches per minute.
the leak should see 5000*1-(44psia/45psia) cubic inches/day or 111 cubic inches/day or .07 cu inches/minute (bubble diameter .5 inch)

This should be easily seen with a soapy solution.

I might be off some, but I think the order of magnitude is right. now right.

If the number has increased, it is likely somewhere there is a change. Rubber tends to get stiffer as it continues to crosslink with age and so seals more poorly, though I do like the idea of clear coat deterioration revealing porosity.

In any case, I think a submersion test will be the most certain to find the nature and extent of the leak path.

Edited because the original calc was as if the entire pressure was relieved from the tire and all the air squeezed out.
Still suggesting submersion.

### RE: Slow leak due to rims, can't find puncture

3DDave - it's like I posted earlier. It can be seen, but you have to be looking for very tiny bubbles, much smaller than the ones coming from a puncture or leaky valve stem. It's been a very long time, but I'd guess that the bubbles I saw from this very condition were on the order of 0.1 mm - no more than maybe 0.2mm - rather than 2 or 3 whole mm.

I think easy to overlook if you aren't looking "small enough". I know I didn't notice them the first time I washed the car that my own leaky wheels had been fitted to. Or the second or third time either. It was almost accidental when I did.

Norm

### RE: Slow leak due to rims, can't find puncture

My experience with porosity in alloy wheels was the bubbles were pretty tiny and tended to cling to the surface of the metal - detaching when they reached a certain size - oh, I don't know. A millimeter?.

The problem was they didn't create anything that could be noticed in a few seconds. I had to wipe the surface of the wheel off when the assembly was submerged and waited to see if I got clingy bubbles later (How's that for a technical term?).

### RE: Slow leak due to rims, can't find puncture

To add a side note, detergent in the water will have a strong influence on how bubbles cling to surfaces. Also, using water that has just come out of the tap can be a problem. Pressurized water before the tap usually has dissolved air that will come out of solution when the pressure is released, causing cloudy water and bubbles that form and cling onto surfaces. Best to start with hot water, in which air has lower solubility, and let it cool. Or boil the water before use.

### RE: Slow leak due to rims, can't find puncture

Not really pertinent to solving the OP's issue, but just some info to consider based on my 20 years with an aluminum wheel supplier and how they managed leak testing....

In the early 90's, this supplier relied on a machinist who was also tending a CNC lathe with robotics as well as visually inspecting and deburring wheels to perform the air leak test. Some lines could spit out up to 30 wheels per hour, which made the leak test a quick and spotty check - no back up leak testing was done. Leak test machines were build with seals around inboard and outboard flanges, the seals clamped the wheels together and then submerged the wheel into a water tank with mirrors around the wheel to assist in identifying leaks. We used small diameter artistic paint brushes to brush away bubbles that clinged to the ridges in the machined surface to both get them to float away as well as see if a new bubble would form (we'd use dabs of grease to mark the area near a suspect bubble). This was done PRIOR to any clear coating (which for this company was NOT a reliable method to seal porosity). Wheels that failed the test were separated and dealt with in the supplier's chosen method (scrapped or repaired) which was approved by the end customer.

Eventually the leak check process was removed from the machining area and a separate department was developed to leak test wheels prior to coating on a mass production level - meaning that's all the department did. This made for a higher quality check and more time could be spent on each wheel - some automation was added to the process to make things as quick as possible. In time, a secondary leak test which occurred after coating and final visual inspection was inserted into the operation. All failed tests were dealt with as described above.

The leak testing department finally decided that submersion in water was affect by each operators level of vision as well as experience in finding small leaks (trained eyes, if you will), so the decision was finally made to abandon a submerged water test and use a more modern helium check. The entire process is basically the same, only instead of just air being pumped into the wheels, helium was pumped in and a helium detection system was created outside the rim. Any escaping helium would flag the wheel to be separated and reinspected manually. This got the majority of GOOD wheels down the line faster and allowed a secondary manual inspection to occur using the water submersion test (to validate that we weren't getting "false positives" for leaks).

While I won't speak for every single supplier, I do feel it's important to note that in my experience any coating applied to a wheel was usually not intended as a cure for possible leakage - it was for the decoration (colored coating of any type) or protection (meaning avoid corrosion, usually clearcoat). Some random testing may find that very small holes were plugged up with coatings but I have always felt that was an unintentional benefit to coating a rim or allowance for overspray in that area. Some wheels are to have 0 coating layers on the rim - most of it is overspray when done on a large scale mass production basis. More coating would drive the price up and I just don't see that as being the norm unless things have changed in 6 years. Please keep in mind, this was just my experience with a single supplier - not all mass pro operations will be 100% the same and some companies running lower volumes might go the extra mile to intentionally coat the rim. They might feel that it improves leak rate pass through, but it's still not 100% effective, as that porosity could (not always) open up over time as the wheel encounters loading and temperature changes.

Just a bit of info to let all the wheel knowledge base know where the mass pro industry has gone over the years in which I was working in it. Again, I don't intend to come off as an authority with a FINAL answer to how a wheel should be checked for leaks, nor how every single manufacturing process will check for them - I am very well aware different companies do things a little differently here and there.

Semi-pertinent to OP:

Equipment might be an issue, but we used all the above posted methods in a lab environment for warranty leak checks - some were so slow that we had to install the tire, air it up to spec and thread a pressure gage onto the valve so we could document the leak rate, then try to find where the leak occurred. These occurrences were very rare but I do not believe we were ever not able to find the leak area or what caused it.

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Enterprise x64 SP1
Intel Core i7 2.5GHz 16GB RAM
4GB NVIDIA Quadro K3100M

### RE: Slow leak due to rims, can't find puncture

Tim,

Thanks for that. I always thought that alloy wheels were naturally porous and the clear coat sealed the pores. Good to find out that is not the case!

I also found it interesting the inspection methods used.

Thanks again.

### RE: Slow leak due to rims, can't find puncture

Capri,

I appreciate you not taking my response the wrong way. My intent wasn't to specifically single you out at all - you have a wealth of knowledge and I wouldn't ever purposefully cut your legs out from under you in a public manner regarding knowledge of wheels/tires.

Simply put, you are right BUT....

There are wheels made that have absolutely no clearcoat - at least about 10 years ago this was true. A certain automaker which has a division based in Australia, took a vehicle from that market, rebadged it for the US and sold it in the US under a different name. Probably not a new concept at all, however, the wheels on the Australian car couldn't be solid as-is here in the states because they had no clearcoat on them at all. I was told there isn't snow to deal with in Australia (at least as much as here in the states) so the warranty returns for corrosion were virtually zero and eliminated the justification for cost of clearcoating the wheel. As a result, the decision was to design a completely different wheel with clearcoat so there couldn't be any mistaking the two (as both wheels would still be manufactured in the same facility near Australia).

I've not dealt with a wheel customer that required the rim area to specifically be coated. I'm sure there are some out there (think higher priced and possibly luxury vehicles), but not any of which I ran across during my time in the industry. I did have an instance where we had to extend the coating area to include the flange and around almost to the tire seating (bead seat) area, but that was to fix a noise issue. The benefits for intentional rim coating usually didn't justify the cost, I'd imagine. There was allowance for overspray on the rim, but the customers typically didn't care if the rim was coated or not. Part of the reason for this is the typical processing of the wheels - they are put on a pedestal with the design face up & moved in a single row through stationary nozzles that can be adjusted, but the nozzles do not move while spraying. The pedestal spins as it moves through several rows of nozzles - I'm sure you could see this on a Youtube video. If you see hand spraying, then that is more than likely a low volume scenario. Both methods have benefits and both have drawbacks as well. Yes, some companies might use robotics in lieu of the static nozzles - but that can be a sizable investment with a slow rate of return, plus adding the manpower for managing/engineering the robots. Point being the static nozzles were above the design face and angled downward and the major OD of the flange prevents the majority of the coating to go beyond the flange.

With all of that said, not all shrinkage/porosity can be sealed with coatings such that it could be considered a reliable and high quality process by which to significantly reduce leakage in a mass production environment. Please keep in mind, I'm referring to hundreds, if not thousands of wheels being processed during a production run. Smaller volumes might be able to pay more attention to coverage and/or amount of the coating, but when it's mostly automated, all of that goes out the window and it's capability and repeatability that matters most while reducing the amount of product being used (yep, all in the name of \$). However, leakers CAN be repaired with certain puttys. No, I don't have enough info out there to offer suggestions for anyone that might ask. I never was fortunate enough to have any experience repairing a leaker but I know it can be done - at least well enough that a warranty claim more than likely isn't an issue after a certain point.

All of my blathering might be a bit dated - new tech has come about and I haven't kept on top of things like I used to do, but that's the way it was for the most part up until the end of 2011 and within the company for which I was employed. Do I think there is any value in coating a rim? A little - most of it is visual - yeah a coated rim (even coated inner rim) does look nice but in doing things that way, you're potentially introducing more problems into the equation - if one decides to paint the ID, will coating get on the mounting area at all? If so, then will there be potential for large drops to get on the the mounting area and cause ride issues? Will coating the rims cause reworked and repainted wheels to have balance issues (think of 1 wheel being processed 15 times before it passes visual inspection)? I've seen wheels with generic paint processing get coating build up to the point that the automaker couldn't get a socket down into the cast in lug holes. A snap decision and lack of process control (counting the number of times a wheel is repainted) was the culprit in that case...but all that is another story.

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Enterprise x64 SP1
Intel Core i7 2.5GHz 16GB RAM
4GB NVIDIA Quadro K3100M

### RE: Slow leak due to rims, can't find puncture

Tim,

I've got some comments, so I will be quoting you so you'll know what I am responding to:

Tim said: I appreciate you not taking my response the wrong way. My intent wasn't to specifically single you out at all - you have a wealth of knowledge and I wouldn't ever purposefully cut your legs out from under you in a public manner regarding knowledge of wheels/tires.

I am very data driven. If anyone has data that contradicts what I am saying, I want to hear about it. I reserve the right to disagree, but at the same time I expect that if our experiences are different, that should be recognized.

We've conversed before. While I have a bunch of background on rubber parts, my interaction with the metal parts is sorely lacking.

Tim said: There are wheels made that have absolutely no clearcoat - at least about 10 years ago this was true. A certain automaker which has a division based in Australia, took a vehicle from that market, rebadged it for the US and sold it in the US under a different name. Probably not a new concept at all, however, the wheels on the Australian car couldn't be solid as-is here in the states because they had no clearcoat on them at all. I was told there isn't snow to deal with in Australia (at least as much as here in the states) so the warranty returns for corrosion were virtually zero and eliminated the justification for cost of clearcoating the wheel. As a result, the decision was to design a completely different wheel with clearcoat so there couldn't be any mistaking the two (as both wheels would still be manufactured in the same facility near Australia).

That would explain why I always thought the alloy wheels NEEDED to be clearcoated. Everything I encountered (here in the US) is clearcoated just to deal with the salt! (Lightbulb goes on!)

Tim said: I've not dealt with a wheel customer that required the rim area to specifically be coated. I'm sure there are some out there (think higher priced and possibly luxury vehicles), but not any of which I ran across during my time in the industry. I did have an instance where we had to extend the coating area to include the flange and around almost to the tire seating (bead seat) area, but that was to fix a noise issue.

Hold on a second! What kind of noise issue were they trying to fix? Here's why I ask.

Over the years, I have encountered a peculiarly isolated series of noise complaints on tires we supply. The pattern was always a particular vehicle - and not other vehicles of the same brand and not other brands of vehicles - AND rim protectors on the sidewalls. Out of all the different makes and models of vehicles we supplied (literally hundreds of makes and models!), it was always one particular size tire supplied to one particular vehicle - and the problem went away after a few years, only to return on a completely different make and model vehicle. Twice I traced this down to the tire rubbing off shards of alloy in the flange area and as the tire rotated, the shards would create this crunching sound.

I've checked with other people that worked for other tire manufacturers and they said they've encountered the same thing.

I've always attributed the phenomenon to heat treating the alloy wheels (Do they do that?) But perhaps the difference is the clear coating?

Can you shed some light on this?

### RE: Slow leak due to rims, can't find puncture

Glad to hear your responses Capri.

In regards to the noise issue, I can only speculate the real cause. I figured it was a tire molding issue that was cheaper and easier to correct by altering the wheel in some manner. In this case, it was simply requiring the tire side of the outboard flange to be included in the normal clearcoat zone. The issue was on a cladded Pontiac wheel but it didn't carry over to the "backbone" wheel which was painted and not cladded and did NOT require additonal paint/clear to be extended behind the outboard flange. It was simply an anomaly to me - never had it happen before or again after that one instance.

As far as heat treatment, yes, all aluminum wheels get it at some point between casting and machining. That's what some of the ID markings in the weight reduction pockets can be attributed to - traceability. Should there be any sort of issue with the wheel that ends up being process related, those markings can lead the "investigation" back to different processes and the dates on which they occurred. Again, I can't speak for all manufacturers, but my former employer recorded specific readings needed to back up their processes (think temperatures, hardness sampling, fluoroscopic x-ray sampling, etc.).

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Enterprise x64 SP1
Intel Core i7 2.5GHz 16GB RAM
4GB NVIDIA Quadro K3100M

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