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A friend has a leaky or flat tire. We looked all over for a nail, screw, or puncture on the tire and couldn’t find the problem. However, when adding air, I discovered that it wasn’t the tire but the valve stem that was leaking on her car. It’s a surprisingly common maintenance problem you can fix at home with a kit from your local auto parts store.

How do I diagnose a leaking valve stem on a tire?

When your tire keeps going flat, but no nails are in it, the valve stem is likely to blame. The valve stem is the part that sticks out that you attach a pump or air hose onto. Inside, a little valve acts like a one-way door for air. However, sometimes the hinges in that tiny door get clogged or bent and start to leak.

The easiest way to spot a leak is to spray some soapy water on the valve stem. If you see bubbles forming, you have a leak. Fortunately, it’s not a huge issue. Most cars have a tubeless rubber snap-in tire valve that is easy to repair.

Can you fix a leaking valve stem?

The most likely culprit is probably the core itself. The core is the metal valve inside the stem. You can buy a cheap valve core removal tool kit at your local auto parts store for less than $10. This tool acts like a screwdriver for the valve, and you can simply unthread it out, according to Family Handyman. The kit will come with a new valve, which you can screw in. Usually, this will fix the issue.

Additionally, it’s always best to jack up the wheel, deflate the tire, and gently remove the core for quick and efficient maintenance. This way, it’s easy to strip the delicate threads.

Can a faulty valve stem be fixed without removing the tire?

If a new core doesn’t fix it, you may need to buy a rubber snap-in tire valve. A car’s rubber seals can often get corroded, or the valve can get loose and leak air. Basically, you need to yank out the old valve and install a new one in your rim. The kit will have directions, but be patient and use some WD-40 to loosen things up.  

The kit will come with a forcing cone, usually some grease, and simple instructions. You’ll force the stem into the rim and then pull it back out until it clicks into the rim. Kits like this cost about $40. The stems come in several sizes, so find a kit with multiple valve stems and closely match up the two.

However, if your car has a TPMS or Tire Pressure Monitoring System, you may be out of luck trying to do this at home. Many systems use a transponder on the inside of the tire connected to the valve. So, if you have a TPMS sensor, it’s best to visit a professional tire shop.

Why are my valve caps green?

Like the colors on gas cans, different colors on valve caps mean different things. My Ram truck tires are filled with nitrogen, and the dealer installed green caps to remind me of that. Generally, most valve stem caps are black, denoting regular air. If yours are green, that is because your tires, like mine, are filled with nitrogen. However, everything else should be the same in the tire.

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Writer - Sedans & Coupes

Dan Mayfield

Dan joined MotorBiscuit in 2022 with over 20 years of experience in journalism and a lifelong passion for anything related to the automotive industry. He grew up wrenching a 1949 Ford pickup truck and an MGB with his dad, learning how not to wire a fuel pump (he inadvertently set the MGB on fire).

After earning a bachelor’s degree in photojournalism from the University of New Mexico, Dan has contributed his expertise to a range of local outlets, including the City of Albuquerque, US Eagle, and the Alliance for Local Economic Prosperity.

On weekends, Dan spends Saturdays enjoying “cars and coffee” chats and, on Sundays, he’s watching the Route 66 Cruise roll through town. He also races motorcycles, and it’s not unusual to find him elbows-deep in his latest cafe racer build.

Taking advantage of the local desert terrain, Dan also enjoys exploring and driving off-road in his trusty Ram Rebel pickup truck, which provides personal insights into his contributions to our Trucks, SUVs, & Crossovers coverage. Dan strives to give our readers unique information about the dynamic automotive market, reading anything that has to do with cars, trucks, bikes, 4X4s, and, in his words, “everything with a motor.”

Dan has earned a number of accolades from the Public Relations Society of America, and is a University of Southern California, Annenberg School of Communication and Journalism Fellow.