Tires: air pressure loss, tire pressure sensors, jeep grand cherokee

Question
QUESTION: I have a 2002 jeep grand Cherokee and a 2007 Lexus es 350. Both vehicles have tire pressure sensors and lose 2 to 4 lbs of pressure per tire per day in cold weather. Per dealer recommendation I let them replace the sensors on the jeep and the problem persists. Any ideas? Also someone said argon gas would help. Is this true? Why? Thanks.    Jim

ANSWER: Jim,

You need to be spending time looking for the leak.  This means immersing the tire (and rim) in water.  Children's pools work well for this.

BTW The gas is nitrogen - and it doesn't fix leaks - which is what you have.

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QUESTION: I have had the above done by two different places with no results. this is all four tires on both cars. I have talked with others with the same problem. A jeep dealership suggested the argon. There must be an answer as the new cars in 2009 will require this sensor.

Answer
Jim,

There is a slow leak and the folks that did the leak test didn't spend enough time looking for it.  They were probably used to looking for fast, puncture type leaks and this is more of a seeping, drip style leak that requires time and patience to find.  That's why I suggested using the kiddy pool to find it.  Since you have had 2 places not succeed, I would suggest you do it yourself.

The leak is likely between the rim and the tire and the fix would be a bead sealing compound, but to be sure that you don't spend any more wasted time, start with the the leak test.  This is the only way to be sure of where the leak is and that will tell you what to do.

BTW it is possible that the leak is through the rims.  Alloy rims are porous and they use a clear coat not only to protect the finish, but only to seal the pores.

BTW, I hope you aren't confusing the normal pressure loss due to temperature drop.  Every 10 degree F drop in temperature results in a 1 psi loss.  So checking your tires when it is 70F out, then checking them when they are 40F, should result in a 3 psi change.  Also, it is not a good idea to check tire pressures when the temperature is below 40F.  Ice can form at 37F under certain conditions and those conditions might occur in a tire valve - the result would be ice holding the valve open.