I had new tires mounted about 2 months ago, and one of them has been leaking slowly since I had it mounted. It usually takes around 10 days for my tire light to go on, before having to fill back up. I went back to the shop 2 times to have it fixed and they said they replaced the TPMS seal and it should fix the problem. It didn't. They then recommended I replace the valve stem. I sprayed up the entire tire with soapy wooder but did not find a single leak. Would it make sense for me to buy a tpms valve service kit and replace the valve? Is it a job I can do on my own? How much should a shop quote me for this? Any pointers are greatly appreciated!

 

I've been a technician with Mercedes Benz 18 yrs and I deal with TPM on a daily basis. Soapy water usually does the trick but If it's a really slow or small leak it can be difficult to find. If you have the capability inflate that tire pressure to around 50 psi ..remove the wheel from the car, and dunk it into a kiddy pool of water submerge the whole wheel if possible. You will see air bubbles. If it's a very slow leak you might have to sit and stare at the tire for leaks. Could also be leaking from the bead where the tire meets the rim or as you stated could be the valve stem. You could also have a pinhole in the wheel itself , I've seen that a few times but I would guess a pinhole in the tire itself.

 

Straight up, defective tire, you didn't have this problem before the swap. If they won't swap it for you, ask them to mount it to a different wheel, we'll see if it leaks in a different location, or if the same wheel leaks. A lot of times with a request like that they'll say, naa, we'll get you a new one and replace this one under warranty.

 

Might ask your tire shop to clean the wheels where the tire bead seals.My 12 has to have one cleaned every couple of years due to corrosion. I live in the south??? Soap will show you where the leaks are.

 

Did they use the sealant around the bead area? I had the leaks in my old Maxima with al rims until I found a shop who used the sealant. Problem solved and never came back.
10 days from 35 psi to 27 psi is not a small leak - imo it is pretty fast. Should not be that hard to find it.
It could be the valve core too. I spit on my index finger after inflating each tire and push it against the valve. If it bubbles, then the core leaks.

 

Thanks for the responses guys!

It will be hard for me to isolate the issue to the tire itself, as on that wheel I also replaced the wheel itself with a used one off eBay, because my old rim bent. The new wheel definitely looked in much better shape than the bent one, and I don't think the wheel is the problem, or at least I hope not. My tpms sensor was moved from the bent wheel to the new wheel, with a new gasket. Tires were bought from tire rack.