How to find a really, really, really slow air leak?

**Brad B** · 08-30-2011, 08:29 PM

About 3 months ago I got new tires on the back of my Carrera. The other day I went for a drive and something didn`t feel quite right. It turns out my left rear tire had about 10 pounds of air in it. They are 305/30-18`s so the sidewall is very short (and stiff) and virtually impossible to see if it is low. After I filled it back up I monitored the pressure and it loses only a pound every few days. Really slow leak.

I tightened the valve stem. Seems ok. Nothing in the tire as far as a puncture. I tried submerging the tire underwater but nothing was obvious.

I hate to take it back to the tire place to fool with because damage to the wheel is so great and it`s always $30 to just look at these fat boys. I am afraid since the leak is so slow that they won`t find the problem.

Any ideas?

**RaskyR1** · 08-30-2011, 08:34 PM

Have you tried putting soapy water over it?

**C. Charles Hahn** · 08-30-2011, 08:40 PM

Originally Posted by RaskyR1

Have you tried putting soapy water over it?

I`m thinking the same... maybe some soapy water, or better yet some sort of gel that won`t evaporate or dry out so you will have lasting evidence of any bubbles forming.

**Brad B** · 08-30-2011, 08:49 PM

Yes, I will try that this weekend. I tried holding it under water with no success. Maybe a soap layer on top will be more obvious. I remember this trick now...thanks for reminding me.

**Dan** · 08-30-2011, 09:11 PM

Max pressure on the sidewall and soapy water everywhere including the wheel itself.

**Bill D** · 08-30-2011, 09:16 PM

Is this a job for a Dawn wash or just regular car shampoo?

**Ron Ketcham** · 08-30-2011, 09:18 PM

May be as many have stated.

Then, again, it may be as simple as replacing the valve core in the stem.

Or, examine the side walls very carefully, looking for a reduction in the side wall material, then the soap and water.

One of my vehicles will have a tire lose air pressure when it sets for a week or so, then I noticed that it only took place when the stem was posistioned in the bottom of the wheel while it sat.

Replaced the valve core stem and no longer goes down.

I will reserve the discussion at this point and my lady friend`s posistions.

Grumpy

**Nth Degree** · 08-30-2011, 10:28 PM

Some dawn is probably the best bet as it will suds up easiest. Most times it is the valve stem. Make sure to remove the cap and spray the inside of the valve too. It may not be seated right. It is also possible that the leak is at the sidewall and only leaks when the wheel is positioned just right to the ground. You many need to slowly roll the car a few inches and be patient since a slow leak like that won`t be obvious the second you spray it.

**Dan** · 08-31-2011, 07:53 AM

I`ve had tires leak because the guy removing the last set didn`t clean the bead area. So don`t forget to lay the wheel down flat and flood the bead area.

**David Fermani** · 08-31-2011, 08:25 AM

Can you overinflate the tire, dunk it and try wiggling the valve stem around to see if it`s coming from there? I`d also hate to risk getting it worked on again, but sometimes a dismount & remount is the only way to fix these issues.

**autoconcierge** · 08-31-2011, 08:56 AM

Per your description me thinks it is the valve stem as mentioned already, thus the reason you are not finding the leak when dunking or even if you spray soapy water on the tire. Pre TPMS valve stems(Such as the one on your 993) can experience this issue.

**Bill D** · 08-31-2011, 11:05 AM

On a somewhat related note, last time my pal from Atlanta was down here, he ran over a really big bolt that stuck pretty bad into his tire. He found a local hole-in-the wall tire outfit that despite its looks, did a great job patching it up. The car`s a Benz, and my understanding is the dealer won`t even do that kind of repair, they`d want to sell you a whole new tire. One interesting thing, since he also did a rotation, this place didn`t rebalance that tire, they marked off where the wheel weights were located on the tire with chalk before they rotated everything. He drove back to Atlanta just fine and that car basically is his mobile office, and he`s had zero problems with the repair. So I`m betting a new valve in Brad`s situation will be a breeze to repair and everything will be better than new.

**noego** · 08-31-2011, 11:51 AM

have you considered or tested for a hairline crack in the wheel?

**jpochile** · 08-31-2011, 01:56 PM

I have a very similar problem with one tire in one of my cars . Actually is a 4x4 Toyota pickup . Since I race enduro motorcycles in the local rallies here in Chile I just put some slime tire sealant on it . Mine is being over a year with no problem

Slime Tire Repair & Sealant 16 oz Bottle FREE SHIPPING | eBay

Cheers , Jean Paul