tire pressure loss

I have a 1992 Accord ex that is loosing pressure in one of the tires.
I fill the tire to 28psi the next day I'm down to 24psi, next day 22psi
this continues until about 18psi and then the pressure loss seems to
stop.The tire has been removed and the mechanic says it's ok.
I have noticed there is a lot of corrosion around the rim of the wheel
next to the tire. Could this be the cause of the problem? If so, what
should I do?

 

BINGO! The corrosion buildup on your rims is likely the cause. I've
run into the same problem on several vehicles - all with alloy wheels.

The cure is to have the tire dealer remove the tire, remove the
corrosion with a wire brush or power wire cup brush, remount the tire
with a goodly amount of bead lube, rebalance and give it a couple years
until you have to repeat the cycle.

It's not universal, I'm told but prevalent enough with the alloy wheels
that the dealers know exactly what to do.

 

I've read in the newpaper's mechanic column that you need to reseal the
aluminum with a clear lacquer;that most aluminum castings are porous and
will leak air if unsealed.
It also prevents the return of the white corrosion.

Using nitrogen for the fill will further slow leakage.
I've read where more shops are now offering this.One I saw offers free
refills.

 

Heard that about the porosity of cast wheels as well.

Any mention of why the nitrogen is used? Does it slow the leakage (hard
to figure that) or more that it slows the formation of corrosion?

 

http://www.automotivedigest.com/view_art.asp?articlesID=19827

Significant Points
1. Proper inflation is key to improving fuel economy up to 3% whatever
used to fill
2. Nationwide fewer than 10% of tire dealers offer nitrogen but number
growing
3. Finding way into mainstream at growing number of tire dealers including
Costco
4. Most dealers charge $2-$5/tire for initial nitrogen fill-up, generally
offer free lifetime refills
5. Improved pressure maintenance important for sensitive automatic
monitoring systems


Background
1. Nitrogen molecules bigger than oxygen molecules so seeps out more slowly
2. Nitrogen resists heat buildup better than air which contains moisture
3. Nitrogen reduces oxidation that can damage tire from inside out
4. Nitrogen is inert gas so no safety or environmental issues

From http://www.mfgdist.com/aircel-n2cel.htm;
Nitrogen maintains tire pressure better.

Oxygen in air is a tire killer. Compressed air contains 78% nitrogen and
21% oxygen. Oxygen in compressed air is very aggressive and reacts
chemically with rubber causing it to lose its elasticity and strength.
Oxygen first consumes the tire liner, then ravages the insulating rubber as
it permeates through the entire casing. This deterioration is accelerated
due to the pressure difference between tire pressure and atmospheric
pressure. In testing, tires inflated with nitrogen lost only 2 psi in a
six-month period, whereas tires filled with compressed air lost six times
as much in the same period. Since nitrogen maintains tire pressure much
longer and will not react with rubber as oxygen does, tire failure is cut
dramatically. With more consistent tire pressure and improved tire
durability, handling for those larger loads is better, too, making your
drivers safer drivers.

 

Then the mechanic is a fool. A tire which is loosing that much air will
certainly show itself in a bubbling water test if said mechanic knows
what they are doing.

Find someone competent.

John

PS Yes, rim corrosion can cause air leaks at the bead and at the valve
stem.

 

yes, but not nearly as much as a small nail embedded in the tread...

 

Change mechanics. He should have solved the problem when inspecting the
tire.

You can find the location of the leak quite easily if you take the wheel
off the car. Put a little dishwashing liquid in a spray bottle, and spray
the solution over the wheel and tire. If it is an aluminum wheel, be
careful not to scratch the face of the wheel; put it on something soft.
With a slow leak like this, it may take a few seconds, but small bubbles
will appear.

Most of these leaks occur on the inside of the wheel. That's because the
inside doesn't get washed, and it is easier for grit and road salt to
build up between the wheel and tire. Corrosion of the wheel creates
a bumpy surface at the bead that allows air to escape. In some cases,
the corrosion will be under the color coat on the wheel, and not
immediately apparent.

A tire shop can fix most leaks like this. They will take a wire wheel
and remove the surface corrosion. Paint would be desirable but it takes
a long time to cure. Until it does, it is not resistant to solvents, and
likely to be wiped away by the tire mounting compound. Tire shop repairs
can be permanent but often last only about six months.

It is important to make sure that the tire is cleaned before
reinstallation to remove any salt or grit on it.

A wheel shop can fix the leaks a tire shop can't. This may involve
removing the finish in the bead area and exposing all of the corrosion.
A quality finish (wet polyurethane or powder coat) will be applied
and the wheel should be like new.

Occasionally, corrosion can lead to deep pits in which case the repair
should be done by a wheel shop.

It is also possible that the slow leak is caused by a bent wheel. Tire
shops can straighten steel wheels; wheel shops can straighten aluminum
wheels.

If it is a steel wheel, your best option might be to simply find a good
used wheel to replace it.
Dan

(This account is not used for email.)