How Do I Find and Stop a Slow Tire Leak?

Although finding and stopping a slow tire leak is best done by removing the wheel and tire from the car, that’s not always practical to do yourself. And since many repairs require taking the tire off the wheel, something not many people can do on their own, taking the car to a tire shop to begin with is often your best option. However, there are some simple things you can check and even correct at home.

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How Do You Find a Tire Leak?

To find a tire leak, your best diagnostic tools are your eyes and a spray bottle of soapy water. Although the leak is likely coming from the tread area, it’s easiest to check the sidewall of the tire first — at least, on the side of the tire that’s facing you. Use your spray bottle to spray the sidewall, bead area (where the tire meets the wheel rim), the rim itself, and both inside (by removing the cap) and outside the valve stem. If air is leaking, it will cause the soapy spray to form bubbles.

While this is quite easy to do on the outside of the tire, there’s unfortunately a 50/50 chance that a problem in any of these areas is on the inside of the tire (except the valve stem). If it’s a front tire that’s leaking, you can gain better access to the inside of the tire by turning the steering wheel all the way to one side or the other, inspecting and spraying what you can see on the inside of the tire, then moving the car forward or backward a little ways and checking again. (Marking the tire with a piece of masking tape can help keep track of what you’ve already checked.) But if it’s a rear tire that’s leaking, the only way to really look for leaks is to remove the wheel, unless you have a raised vehicle you can crawl under.

If you haven’t yet found the leak, it’s time to look at the tread. First, visually check the tread for nails or screws (note that they’ll often be worn down to be flat and shiny) and spray the tread with the soapy mixture. Unless you jack the tire off the ground, checking the tread requires moving the car forward or backward a short distance at a time to inspect all the way around the tire. If you have someone who can drive the car very slowly while you look at the tread, great; just make sure they’re driving away from you, not toward you. (You’ll be down low, so they won’t be able to see you.) If you’re moving the car yourself, marking the tire with chalk, a pencil or a little piece of masking tape will tell you where you left off.

If you find a nail or screw in the tread, your instinct might be to grab it with a pair of pliers and pull it out, but keep in mind you will be creating a large hole that will turn your slow leak into a very fast one. This is really only a good idea if you have a tire plug kit at the ready to plug the hole, along with an air pump to inflate the tire afterward.

If you can remove the wheel, the best way to find a leak is to submerge the tire in a dunk tank, which only has to be deep enough to cover the wheel rim — roughly 4 to 8 inches, depending on the height of the sidewall. While a bathtub works great for this (as you can roll the tire and still keep the bottom submerged and even add in a little liquid soap while the tub is filling), other possibilities include a dish pan, a large plastic storage tub or a drawer from plastic storage shelves.

Tip: Sometimes, the tire will only leak if it’s resting in a certain position — for instance, with the nail at the bottom against the pavement. (A sidewall crack can do the same.) This often results in periodic leaks, in which the tire will sometimes go for days without losing air, then one morning it’s low, only to repeat after you fill it with air. If this seems to be the case, note the position of the tire when it happens — maybe with a marker or piece of masking tape at the top — to see if less air leaks out when the mark is not at the top.

How Do You Stop a Tire Leak?

There are four areas where a tire leak could occur: the tread, sidewall, wheel rim and valve stem.

Tread

Without taking the tire off the wheel, a hole could be plugged with a tire plug kit, which usually costs less than $15. To plug the hole, remove the offending nail or screw, use the included round file to make a round hole if needed, then fill the hole with a rubber plug using a special tool. A tire shop may do the same thing, though they might also dismount the tire and put a patch on the inside.

Sidewall

Old tires can develop cracks in their sidewalls, and these cracks can leak out air. Cracks can also develop by hitting large bumps or by driving on the tire when it’s low on air or flat. In most cases, leaks in the sidewall can’t be repaired, so you’re looking at buying a new tire — or possibly two or a whole set.

Wheel Rim

Especially in areas that use road salt in the winter, the wheel can corrode and cause leaks at the mating surface between the wheel rim and the tire. These leaks could also appear in the metal or aluminum wheel itself, often for the same reason. The former usually requires removing the tire from the wheel and cleaning up the mating surfaces, while the latter may mean having to buy a new wheel.

Valve Stem

The valve stem — where you put air into the tire — can leak due to cracks in the side of the stem, a sealing issue between the base of the stem and the wheel, or internally due to a leak in a tiny removable valve called the “core.” (This valve allows air to go in when you inflate the tire but is not supposed to let the air get out unless you press down on a little post.) Only the last issue is easily rectified at home, as the stem is typically installed from the inside of the wheel. A special tool that is sometimes built into the top of tire caps can be used to unscrew the core, allowing you to fix the leak by either cleaning the core or replacing it. 

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What Is the Tire Sealer Option?

Tire sealers are a liquid or foam that’s pumped into the tire through the valve stem to seal small leaks. Some tire sealers come in a spray can filled with sealant and compressed air, with a hose or nozzle that screws onto the valve stem. It’s intended to be used on a flat tire to seal any small leak and partially inflate the tire so you can drive on it, though you should only drive slowly and not very far due to the low tire pressure. Other sealers come as a liquid that’s squirted into the valve stem (you sometimes have to remove the core first), then you inflate the tire with a pump.

While great in theory, tire sealers don’t usually work with anything but small holes (which is what you’re trying to seal in this case), and they usually don’t work as well for leaks on the sidewall, rim or valve stem. Tire sealers also leave a sticky mess inside the tire that can gum up tire pressure sensors (if your car has them; they relay the tire pressure to the car’s computer), and it has to be cleaned out by the shop before they can fix the tire. Some are flammable, too, so if you use a sealer, make sure you warn the tire shop that you’ve done so.

There are also tire-sealing kits that include liquid sealer and an electric tire pump (that usually plugs into the car’s power outlet), often in the same unit. Many new cars come with these in place of a spare tire. The kits tend to be a better all-around choice, if for no other reason than you can inflate the tire to its intended pressure. Furthermore, the pump can be used to top off tire pressure when it drops in the winter due to the colder air. (Cold air takes up less space than warm air, reducing tire pressure by roughly 1 pound per square inch for every 10-degree drop in air temperature and causing the tire pressure warning light to illuminate on the first cold day of winter.)

While a slow tire leak can be annoying and tricky to find, it sure beats having a blowout.

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