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I have a strange tire pressure issue, I put my C7 GS into hibernation on 11.01, filled the tires up to 35 PSI for the duration. On 12.14 I noticed that the driver side rear tire seemed really low, checked it with my digital gauge and it registered 15 PSI, filled it up to 38 PSI with the plan of filling it every week until I could drive it to the tire shop and have it checked out this Spring. Well, five weeks later it is still at 38 PSI, anyone have any ideas how it could go down 20 PSI over six weeks, and then have it remain stable at 38 PSI for five weeks?
If all is as you say, the only thing I can think of is that for some reason the Schrader valve didn't seal completely when you aired them up the first time and it did the last time. That's just a s.w.a.g. though...
Last edited by Ed Ramberger; 01-19-2018 at 07:33 PM.
Maybe the tire lost air around the bead from sitting and airing it up to 38psi reseated the bead well enough that it has stayed sealed at the higher pressure.
I assume you have not driven the car at all during this time.
Maybe you have a leaky valve stem and the cap was not initially put on very tight. After you filled it up you may still have a leaky valve stem but the cap is now put on tight and is keeping the air in.
If you moved the car after you put air in it, you may be resting on the nail/screw or whatever that has put a slow leak in it not allowing air to escape.
I have a strange tire pressure issue, I put my C7 GS into hibernation on 11.01, filled the tires up to 35 PSI for the duration. On 12.14 I noticed that the driver side rear tire seemed really low, checked it with my digital gauge and it registered 15 PSI, filled it up to 38 PSI with the plan of filling it every week until I could drive it to the tire shop and have it checked out this Spring. Well, five weeks later it is still at 38 PSI, anyone have any ideas how I could loose 20 PSI over six weeks, and then have it remain stable at 38 PSI for five weeks?
You're going to need to verify the accuracy of your TPMs, if you have OnStar verifying your tire pressures.
If not, you're going to have to have the tire inspected off the vehicle.
The car has not been started, or, moved since 11.01, tires are in the exact same spot since then. My digital tire pressure gauge is very accurate, and conformed exactly to the computer and OnStar data when last driven.
I will check the valve stem and see if the Schrader valve somehow came loose.
BTW, after seeing the size of the GS 335 tires at the time of purchase last June, I decided to purchase the wheel and tire insurance plan through my dealer, I am therefore covered in the worst case tire replacement scenario.
I would bet on the Schrader valve core either being loose or not seating due to a piece of debris. When you check your tires a small amount of air is vented through the valve and bad luck of the draw sometimes means a bit of debris in the tire stopped on the sealing surface as the valve closed. The next time you added air the income charge cleaned the seat.
I would bet on the Schrader valve core either being loose or not seating due to a piece of debris. When you check your tires a small amount of air is vented through the valve and bad luck of the draw sometimes means a bit of debris in the tire stopped on the sealing surface as the valve closed. The next time you added air the income charge cleaned the seat.
Another possibility. The valve cap!
Bought some cheap valve caps for my 2014 because they had a carbon fiber look on top. They did not have the small rubber “O” ring inside the cap.
Paid ~$35 for Jake valve caps for the Grant Sport. They are metal not plastic and have the “O” ring. If the Schroeder valve has a very slow leak, the. “O” ring and tight cap can stop it.
If your wheels are anything like my 2014 with chrome wheels the valve stem has a 12 mm nut that is around it. A couple of years ago I am 50 miles from home and the the car announces my front left tire is low. The darn nut is loose and the tire is flat. I now carry a socket in the trunk just is case and periodically check the tire nut for tightness. If that nut gets loose you will lose air and nothing in the owners manual will alert you to that fact.
Correct torque for the nut is very low, something like 60-70 inch pounds.
I check mine once per year with a low range torque wrench, typically takes 1/4 turn or so each year even with no leakage.
I would also guess the valve stem did not seat properly when you aired it up the first time. Keep an eye on it, you can test it by taking the valve stem cap off, put some spit or some soapy water on it to test it. While you are at it spray some soapy water around the valve stem seal at the wheel where they meet.
01-19-2018, 07:14 PM
Strange tire pressure issue.
