I found this thread, but the installer could not confirm any leakage from the valve stem area....

http://www.rx8club.com/showthread.php?t=72785&highlight=leaky+tire

Okay, so I got a leaky tire. Took it back to the installer, they checked it, did the bucket test, couldn't find anything. They took the tire off the rim and polished off the old rubber from the rim where the bead sits and remounted, put in a new core, no improvement.

Here are the facts:
Goodyear Eagle 225/35/18
18X7.5 alloy wheel
TPMS

Installed late Jan/early February when we were still having the warm weather, problem started when the cold snap occurred.

Pump the tire up to 32 lb, down to 18 by next morning

What could it be? A crack in the wheel? Or simply the low profile configuration doesn't agree with cold weather and it should go away as things warm up? Or the TPMS?

I need to go into the dealer for some warranty work soon anyway, I'll probably have them check the seal on the TPMS.

If that doesn't work my backup plan is Slime...A couple years ago I had a similar "mystery" leak on my minivan. After about 4 cans of Fix-a-Flat it went away. I know the Fix-a-Flats have a reputation for ruining the tires. What about the "Slime", the green gunk you either pump in, or remove the core, squirt in, re-core and pump? Claims its safe for tires. Or will these screw up the TPMS?

[QUOTE=pcimin will these screw up the TPMS?[/QUOTE]
Yes, and your tire balance, and your relationship with whoever works on it after this.

I wouldn't be drivin around on a leaky tire, especially if you're getting that much deflation over night. You're risking a blowout everytime you get in it. The last thing you want is to be going into a bank and then BOOM you're ass swings around and you ram into something.

The gunk that Mazda issues with our cars binds to the rubber in such a way, you kill the tire when you use it.

My advice: Get to the dealer ASAP and explain your situation and get a good tire.

just mix some dish or car wash soap in water and pour/spray it on the tire, the leak will show itself, you must have taken it to some real goobers for it to leak that fast and not be found

Same thing was happening to my car when i had the wheels put on. If you have 18's or higher this is what i would reccomend:
tighten the air nozzle (where you put air in it). The base of it is what holds on the electronic tire guage and sometimes it gets loose. If its tight, then i would say get some bead sealer and put it around the rim and the air nozzle. hope this helps.

I would not recommend trying to tighten that until you determine it's where the leak is, the soap bubble test will reveal it clearly if if is. Those TPMS devices break easily if you overtighten it.

Thanks. It does appear to be related to cold weather. When the temp is about 30 F, no leaks. When the temp drops to below 25 or so at night, that's when it leaks. I'm assuming it's the seal around the TPMS, I'll try the soapy water if it gets cold again.

Hopefully not much cold weather left this year.

I had a similar problem with my TPMS. The thing was too tight, backed it off just a little and the leak went away. 4800 miles on that tire, no leak.

I've got the same problem too...I tightened and loosened the stem core with no luck...

I'm gonna take it out one day and put teflon tape on it and put it back in. until then I'll just refill my tire every couple days lol