Low Tire Pressure Indicator

Over the past year, the low tire pressure light on the dashboard came on, usually about every 4-6 weeks, always on cold mornings when one would expect tire pressure to be low. About 85% of the time, it was the left front. I was usually down between 6 and 15 lbs. (According to the label on the door, the tires require 33, but I can never get the light off with less than 36 – which is what the dealer recommends. Also, as the front tires I just replaced had 84K, I don’t think 36 is excessive). And, I always have to add air – even after the tires become warm from highway driving, the pressure never rises to the point that the light goes out.

Anyway, I just replaced all 4 tires on November 21st – less than 4 weeks ago. Since then, the low tire pressure light has come on 5 times – once at 20 psi and the rest at 30 psi - always the left front. I took it to the dealer last Saturday – all they could find was that the valve stem was out of position. No leaks, no punctures, no problems with the wheel. Lo and behold, the left front tire was down again yesterday. While I understand that it is possible that a tire may be low on a cold morning, I would expect this to happen both more frequently, and to the other three tires as well. What is going wrong here?

The air is obviously going somewhere. I’m betting you have alloy wheels and the one losing air is slightly out of round. This happens more frequently with alloy wheels because they’re softer than steel.

If it’s a common car with standard wheels, you should be able to find a replacement fairly cheap.

Take the wheel off, spray the tire with soapy water (especially around the valve stem and the bead), and look for bubbles. With a leak this big, you’ll almost certainly find it.

My guess is that you’ll find the leak at the bead, due to corrosion of the wheel in that area.

Also ask them to do a close inspection of the valve stem hole on the rim. Your looking for a small pitted spot. These can pass the shop bubble test and then start leaking again (very slowly) once it’s back on the car. Often when they do the bubble test they will goose it to max psi so they get a fast result. This can seal the leak and they miss it. Had this problem twice. Both cases the tire went to 20-21 lbs. and stopped leaking. They smooth out the pit and your done. Your rim could also have built up crud to scrape off where the tire bead seats, but think they would have seen that.

Sometimes it’s hard to get a good seal on certain alloy wheels, especially older ones, or it’s possible the wheel itself may be leaking.

I’ve had similar problems in the past.

SOMETHING is leaking, and it’s localized with that one wheel. A good tire shop should be able to find and fix the leak.

Yup, our friends in China (home to lead-encrusted toys and poison dog food, among other delights) also foisted a huge number of defective tire valves on the US public a couple of years ago. It seems that the Dill Co decided to outsource their production to China, with very bad results.

While the recall of these defective valve stems took place over a year ago, it is possible that your tire dealer allowed one or more to slip through the cracks.

Take a look at:

Did you get new service valves when the tires were replaced? If not, you might try that. You can buy replacement service valves at any auto parts store. The service valve is the valve that opens when you put air in the tires. You can also buy a tool to take the old one out and screw the new one in. It’s cheap and worth a shot.

Makes sense, as that wheel has been prone to air loss for some time.

The dealer did that. Plus the car is only 2 1/2 years old and I see no evidence of corrosion.