40,000 miles . 2 of the tires will not hold air. My mechanic put 80 lbs. of air in them and could not find a leak. They are Continentals and came with the car. Do I need to replace them? Help!
You said mechanic. This is a tire shop problem . At 3 years and 40000 miles it is possibly replacement time .
It could be the valve stems, it could be porosity in the wheels. I’d lean to porosity in the wheels. But given the tires have 40K, install a new set of tires. If any leak afterwards, have the wheels coated to seal them. The tire store should know what this is and have it on the shelf.
Remove the wheel and clean it off w/soap and water, then rinse with plain water. Next lay it on the ground horizontally, so it is perfectly level, wedge it here and there as necessary. Inflate to normal pressure. Now use an old paint-brush to paint some warm soapy water on the tire and wait a few minutes to see if any air bubbles start showing up. Paint the valve stem area, the rubber part of the tire, along the entire bead, and the rim. If you see no bubbles forming, turn the tire over and do it all again.
Beyond that you’ll have to put the entire wheel in a big tub of water. That will catch the source of any leak at all.
Frustratingly, many tire places (and mechanics too) are dismissive of small/slow leaks. It’s just too much time to spend and too low profit to do.
If hole is as big as needed to pass a train, they would patch it, otherwise it is “we do not see any issue”.
A few times I needed to go with “soapy water” method @George_San_Jose1 mentioned above (although will less preparations) to find slow leaking area, mark it with sharpie and then go back to tire place and point them where to patch.
Wow. This is why you don’t have a “mechanic” work on your tires. At least this particular mechanic…