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How Do You Tell If a Valve Core Is Leaking?

Take the cap off, spray Bubble Check into the open end of the valve stem, and watch. Bubbles that keep building mean the core is leaking.

2 min read CHAOS Moto

To tell if a valve core is leaking, take the cap off, spray Bubble Check into the open end of the valve stem, and watch. If bubbles or foam keep building at the opening, the core is leaking. Snug the core with a valve core tool, spray again, and replace the core if the bubbles come back.

Find your leak in 3 taps: Leak Lab →
Wheel diagram: red circle around the valve stem with bubbles forming at its open end Valve core leakSPRAYOpen end of the stem,cap offLOOK FORA bubble that keepsgrowing at the openingNEXTSnug the core, retest,replace if it still leaks
Valve core: cap off, spray the open end of the stem. A leaking core keeps blowing a bubble at the opening.

How does it show up?

  • A slow pressure loss with nothing in the tread and a clean bead.
  • It starts after a pressure check or after air was added.
  • The cap was missing and dirt got into the stem.
  • The core was loosened or swapped during TPMS or tire service.

Where do you spray Bubble Check?

  • The open end of the valve stem, with the cap removed.
  • Spray enough to cover the opening so a bubble can form across it.

What do the bubbles look like?

  • A bubble that forms across the opening, pops, and forms again.
  • Foam that keeps growing at the mouth of the stem.
  • No bubbles after a minute or so usually means the core is sealing.

What do you do next?

  1. Snug the core with a valve core tool. On a TPMS stem, follow the sensor maker's core torque spec.
  2. Spray again.
  3. If it still bubbles, replace the core. On TPMS stems, use the core the sensor maker specifies.
  4. Reset the pressure, reinstall the cap, and spray once more to confirm.

How to run the check

  1. Inflate the tire to its specified pressure. A soft tire may not push enough air to show a slow leak.
  2. Spray Bubble Check on the area and give it time. A slow leak can take a little while to show.
  3. Watch for bubbles that keep forming at the same point. The first light foam from the spray settles; a leak keeps building.
  4. Mark the spot with a tire crayon before you wipe the area dry.

About Bubble Check

Bubble Check is the CHAOS Moto spray-on tire leak detector. It comes in a 32 oz bottle with a trigger sprayer, so you check the tire on the wheel with no dunk tank needed. Shops use it to pinpoint valve and bead leaks and for TPMS stem checks. See the Bubble Check page or where to buy. Bubble Check is not currently sold on Amazon.

Common questions

Should I replace the valve core or the whole stem?

If the bubbles are only at the opening, start with the core. If they show at the base of the stem or the rubber is cracked, see the valve stem and TPMS stem guide.

Do TPMS valve stems use a different valve core?

Often, yes. Use the core the TPMS sensor maker specifies and tighten it to their spec.

Does a valve cap stop a leak?

A cap keeps dirt and moisture out of the stem. Fix a leaking core rather than relying on the cap.

More leak types in the Leak Lab. Related: valve stem and TPMS sensor stem leaks and using Bubble Check on TPMS, valve stem, and bead leaks. Questions: sales@chaosmoto.com or 480-829-7888.

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