Lord Howe changing the rear wheel of his Bugatti car in 1930 while driving with Captain Malcolm Campbell during the Double Twelve Hour Race on the motor racing circuit Brooklands. United Kingdom. Slow leaks have always been an annoying problem, but you can use soap to find a slow tire leak or valve stem leak. | Imagno/Getty Images

Using Soap To Find A Slow Tire Leak Or Valve Stem Leak

Checking and adjusting your tire pressure is key to proper vehicle maintenance. If your tire pressure is dropping between your tire pressure checks, you have a slow tire leak. Learn how to find your leak...

by Henry Cesari

Published on October 7, 2021 10:50 pm

3 min read

Checking and adjusting your tire pressure is key to proper vehicle maintenance. If your tire pressure is dropping between your tire pressure checks, you have a slow tire leak. A puncture in a tire’s rubber can cause a slow leak. Faulty valve stems also cause slow tire leaks. Finally, a tire that is not sealing against the rim properly will leak. Lucky for you, you can easily diagnose your slow tire leak at home.

You can use soapy water to find a slow tire leak

Jack up your vehicle, being careful to support it safely on jack stands as well as your jack. Then remove your tire.

Next, mix a little dish sope in water. If you have an empty spray bottle, pour your mixture into the spray bottle. Then simple spray the mixture on your leaking tire. If you don’t have a spray bottle, you can pour a thin layer of the solution over your tire.

Don’t miss the edge of your tire, where it seals against the rim. You will need to slowly roll your tire to pour water over its entire surface. As you do this, look for rapidly forming bubbles that indicate escaping air.

Finally, pour a little of the solution over the valve stem. The valve stem is where you fill the tire and check your tire pressure. Make certain to pour the soapy water over the seam where the stem enters the metal rim’s metal. Read more on finding a tire leak.

Types of slow tire leaks: air escaping between the tire and rim

World speedway champion Barry Briggs repairs his motorcycle in the pits at Wembley, London, in 1958. Slow leaks have always been an annoying problem, but you can use soap to find a slow tire leak or valve stem leak. | Fox Photos/Getty Image — Repairing a motorcycle | Fox Photos/Getty Image

If you find air escaping between the tire and the rim, you know the tire is not sealing. This may be because the edge of the tire is damaged. A dirty or rusty rim sealing surface can also cause a slow leak. Finally, if tire was improperly mounted it will leak.

The “bead,” or sealing surface of the tire, should pressed against the rim by the air pressure in the tire. To set the bead, a mechanic stretches the tire onto the rim, then inflates it to maximum PSI. Finally, the technician strikes the tire tread or bounces the tire on the ground like a basketball. This impact seals the rubber against the metal.

Types of tire leaks: air escaping through the sidewall

A man kneels outdoors to change the front tire on his Model 'T' Ford in 1915. He is demonstrating one of the first models with replaceable tires. Slow leaks have always been an annoying problem, but you can use soap to find a slow tire leak or valve stem leak. | Camerique Archive/Getty Images — Changing a Model T tire | Camerique Archive/Getty Images

If air is escaping through the tire rubber, it has a puncture or tear. If the air is escaping through the sidewall, the tire is unsafe for highway use. Driving and cornering places more strain on the tire’s sidewall than a patch can support. If you try to patch the sidewall, you risk a dangerous blowout.

Types of tire leaks: air escaping through a puncture in the tread

A view of two Laing workers carrying out maintenance work on the rear right wheel of a Fordson Major Diesel Tractor. Slow leaks have always been an annoying problem, but you can use soap to find a slow tire leak or valve stem leak. | Hulton Archive/Getty Images — Changing a tractor wheel | Hulton Archive/Getty Images

If air is escaping through the tread of the tire (the part of the tire that contacts the road), it might be repairable. Most tire shops or auto repair shops will be able to patch a tire with a tread puncture cheaply. Many tire technicians prefer removing a punctured tire from the rim and patching it from the inside, instead of plugging it.

If you would like to fix the tire yourself, you only need a tire repair kit. A basic kit with plugs will set you back $15-$25. First deflate the leaking tire completely. Then remove any debris still inside the puncture. Next, use a round file to turn the puncture into a larger, uniform hole. Finally, press a sticky rubber plug through the hole, and cut off the end of the plug. It is a simple process you can complete in an hour if you are a dedicated DIYer. Learn more about plugging a leaking tire.

Types of slow tire leaks: air escaping from the valve stem

A man changes a tire in the Lion enclosure in Windsor Safari Park in 1970. Slow leaks have always been an annoying problem, but you can use soap to find a slow tire leak or valve stem leak. | Central Press/Getty Images — Changing a tire with an audience | Central Press/Getty Images

If you find air escaping from the cap on the valve stem, then your valve mechanism is damaged. Many tire repair kits include replacement valves. With a new valve, you will be able to replace your malfunctioning valve in minutes.

To replace your valve, you first deflate your tire. Then, use your kit’s valve tool to screw out the old valve and screw in a new one. Finally, reinflate your tire and make certain it holds air. Learn more about valve stems with a tire pressure monitoring system attached.

If air is escaping between the valve stem and rim, your tire must be removed before the valve stem can be replaced. The good news is that the professionals at an auto shop can replace your valve stem quickly and cheaply.

Staff Writer

Henry Cesari

Henry Cesari joined MotorBiscuit in 2021 and brings his deep interest in vintage cars, trucks, and motorcycles to the site. Having restored his first classic car at just 16 years old, Henry has wrenched on everything from overland campers to Japanese motorcycles and even pre-war Bugattis. Henry is also an avid attendee at local car shows and genuinely enjoys connecting with fellow auto enthusiasts.

Henry earned a Bachelor’s in Anthropology and English from the University of Vermont. He has since incorporated his love of the written word with his admiration of classic cars. While Henry is interested in vintage cars, he believes the golden age of cars is yet to come. He is confident journalists will play an important role in this revolution by exposing the industry as it is now and envisioning its possible future.