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How to Find and Fix a Slow Leak in Your Tire

Stephen Fogel
April 13, 2018

slow leak in tire

A slow leak in one of your tires can be really annoying. Who wants to stop at the gas station every few days just to use the air hose? The truth is, driving on underinflated tires is more than a nuisance — it’s dangerous. 

Not having enough air in your tires can force their components, including rubber and steel, to be damaged by flexing too much. In a worst-case scenario, these weakened components can combine with added heat to create a blowout, which can easily cause you to lose control of the car and end up in a wreck.

So, it’s a good idea to check your tire pressure every couple weeks to stay on top of any potential leaks. Let's look at what causes a leak, or you can skip ahead to learn how to find the source of one and how to fix it.

What is a slow leak, anyway?

A slow leak is a problem that results in your tire losing a small amount of air pressure on an ongoing basis. If you check your tires often, you’ll detect this problem soon after it starts. You may notice it as a slight drop in pressure in one tire. If you have a model year 2008 or newer vehicle, your tire pressure monitoring system (TPMS) warning light will come on when your tire has lost 25% of its normal pressure.

The first time this happens, you would inflate the tire back to its normal pressure and go about your business. But the next time you check your tires, you notice the pressure loss in the same tire again. Your TPMS may light up again. What’s going on? 

What causes a slow leak? 

A slow leak can be caused by a number of tire problems:

Your tire has been punctured

This is usually the result of a nail or some other piece of hard, sharp road debris. When you drive over it just right, the weight of your vehicle can push it through the tire and cause the air to then leak out slowly.

Your valve stem is leaking

The valve stem is the cylindrical rubber piece that attaches to each wheel. It’s the place where you can add air to the tire and also check its pressure. The stem itself can leak where it attaches to the wheel. It can also be broken, cracked or cut.

The spring-loaded valve inside the stem opens when you inflate your tire or check the pressure. It should stay shut at all other times, in order to keep the air pressure in. If the valve itself is loose, damaged, defective or overtightened, air can leak out slowly.

Your wheel has been damaged

Your wheels are always exposed to the elements and a hostile road environment. Your wheels can be bent or damaged by an impact, eaten away by corrosion, or become porous over time due to age and poor manufacturing quality. Any or all of these conditions can be responsible for a slow leak.

Your tire bead has been damaged

The tire bead is the part of the tire that touches the wheel and seals the air in. It’s thicker and is reinforced with steel cable for extra strength. The bead can get damaged due to bad tire installation, a piece of road debris or decomposition of the rubber on an older tire. This leads to a slow leak between the tire and the wheel.

How to find a leak in your tire

The source of a slow leak can be hard to find. If your tire was punctured, there may be a very thin nail stuck deep in the tire tread, or the object may no longer be in the tire at all. If the problem is the wheel, the bead or the valve stem, the problem spot may not be visible. Here are some ways to track down the source of your leak.

Do a visual inspection

Take a close look at the wheel and tire in question. Does the sidewall or the tread have any obvious slashes, cuts, perforations or objects sticking out? Move your vehicle a slight amount to get the tread on the bottom up to the top, where you can get a better look at it. Turn your steering wheel completely to the left, and then the right, to get a better look at the inside surface of the tire. If you see anything that looks like damage, mark it with a piece of chalk on the sidewall so that you can find it later.

Listen for the hiss

You can do this at the same time as the visual check above. Park your vehicle in a quiet place and shut it off. Listen closely and see if you can hear the hiss of air. If you do, try to locate the exact location, then mark it on the side of the tire with chalk. If you don’t hear anything, move your vehicle forward or back one-half of a tire revolution. This will move the part of the tire that was on the bottom to the top. Listen again for the hiss, and mark its location on the sidewall. If you don’t hear a hiss, move on to the next step.

Use the soapy water method

This requires a spray bottle that contains a solution of four parts water to one part dish soap: 

  • Spray the soapy solution all over the valve stem. See if any bubbles form — this will usually identify the source of the leak. 
  • Spray the solution all over the area where the tire meets the wheel, both inside and out. Look for bubbles. If you don’t see any, it’s on to the final place to check. 
  • Spray the solution liberally on the tire sidewalls and the tread. Check in all the narrow tread crevices. Be thorough and look very closely for those telltale bubbles.
  • Once you identify the source of the leak, mark it on the tire.

Next level: Take off the tire

While it’s not necessary to remove the affected wheel from your vehicle to use the two methods above, doing so will give you much better access to the entire surface of the tire.

Park your car on flat, hard (paved or concrete) ground. Be sure to securely block your vehicle’s wheels and apply the parking brake. Then loosen the lug nuts or bolts on the affected wheel before you jack up your car. Once you’ve raised your wheel clear of the ground, unscrew the nuts or bolts, and remove the wheel.

Submerge the wheel and tire

If you take the tire off, this is another way to check for a leak. You’ll need a container large enough to fill with water and submerge at least part of the wheel and tire in. A child’s wading pool works very well for this.

Simply place your wheel and tire completely underwater and look for air bubbles escaping from the tire or wheel. Once you see the bubbles, mark the location of the leak and put the tire (or a spare) back on the car, being sure to secure it properly.

If you don’t want to do it yourself

If you’re having trouble finding the source of the leak, or don’t feel comfortable taking the tire off your car, take it to your mechanic or a tire shop. They should be able to find the cause.

Get it diagnosed by a professional
 

How to fix a slow leak

Once you’ve found the source of the leak, it’s time to fix the situation. Sometimes a simple repair is all that’s needed, or you might need a replacement

Fixing a tire puncture

Simple and small punctures in the tread can typically be repaired, as long as the tire hasn’t been driven on when flat. This can be done either with a patch on the inside of the tire (which requires removing the tire from the wheel), or with a plug (which can be applied from the outside of the tire).

If your puncture is large, or it has damaged the shoulder or sidewall of your tire, it can’t be repaired safely. You will need to buy a new tire.

Fixing a leaking valve stem

If the problem is the valve mechanism itself, known as the core, it can be replaced with a new one. A valve core tool is required to remove the bad core and install the new one. If you do this yourself, be sure to wear eye protection. Use the valve core tool to make sure that the inside threads are clean before you install the new core.

If the rubber valve stem itself is cut, damaged or leaking where it is attached to the wheel, it will need replacing.

Fixing a damaged wheel

Many bent or damaged wheels can be repaired at a wheel repair shop. Your mechanic can probably recommend one in your area. If the damage is too severe to be repaired, you’ll need to replace the wheel. Your mechanic may be able to repair corroded wheel surfaces that cause an air leak. Porous wheels may require replacement, however.

Fixing a tire bead problem

If your tire bead-related problem comes from a bad tire installation, or a piece of debris stuck in between the wheel and the tire, this can usually be fixed by dismounting the tire, removing any debris, and then remounting the tire. If the leak was caused by rubber decomposition or a defect in the bead area, then you’ll probably have to replace the tire.

» MORE: Find a shop that can work on your tire issue

Tire sealant vs. a spare tire

Many modern vehicles no longer come equipped with a spare tire and wheel. A recent AAA study found that 28% of 2017 models didn’t come with a spare. In the quest to reduce cost and weight, and improve fuel economy, many manufacturers now provide an aerosol can of sealant intended to seal the tire and inflate it. This is not ideal.

If your tire blows out, the sealant will not fix it. If you damage the sidewall, the sealant won’t help. Plus, the can of sealant expires in four to eight years, meaning it might no longer be good when you need it. 

Some manufacturers offer a spare tire and wheel as an option when you buy your vehicle. You can also get a spare from a tire dealer. This is definitely something worth considering, especially if you spend a lot of time on the road or live in a remote area. 

Why proper tire pressure is important

Making sure that your car’s tires are properly inflated is important for several reasons:

Your safety

Without the right amount of air pressure in the tires, your vehicle will not perform well. It won’t be able to corner, accelerate or stop the way it’s designed to.

Then there’s the issue of tread separation and blowouts. A blowout on the highway can be extremely dangerous.

Supporting your vehicle

Your car, truck or SUV weighs several thousand pounds. The compressed air in your tires is what supports all that weight as you travel down the road. When your tires lose their air pressure, your vehicle loses its ability to support and carry that weight. 

The lifespan of your tires

The air in your tires acts as a cooling system, dissipating the heat that is produced as your tires accelerate, corner and stop. Heat is your tires’ enemy, and low pressure allows the heat buildup that can cause a blowout or other tire damage.

Your fuel mileage

Low tire pressure takes a toll on your fuel economy. Lower pressure means more rolling resistance, so it takes more energy to get and keep your tires rolling. This wastes fuel — and your money. 

 

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

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