How to Use a Vacuum Gauge

Written by matt koble
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How to Use a Vacuum Gauge
A vacuum gauge (engine image by goce risteski from

A vacuum gauge is a versatile and handy tool to help you measure engine vacuum. Your car's engine creates a vacuum effect to run many of your car's accessories, such as the heater, air conditioner and cruise control function. When attached, your vacuum gauge should read between 14 and 18 inches. Less could mean anything from a broken or backed up line to your ignition firing too late.

Skill level:

Things you need

  • Engine vacuum testing kit

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  1. 1

    Turn the car off and allow the engine to fully cool. Pop the bonnet and free one end of the vacuum source you'd like to test. This includes many manifolds, the PCV hose, the power brake vacuum hose or any other vacuum line.

  2. 2

    Connect the vacuum source's free end to the vacuum gauge. Turn the car on and allow the engine to idle.

  3. 3

    Inspect the face of the vacuum gauge to ensure the readout is between 14 and 22 inches of vacuum. Experts disagree on the exact numbers that denote a healthy engine; suggests a range from 14 to 18 inches, while suggests up to 17 to 22 inches.

  4. 4

    Turn the car off and let it cool for a few moments. Disconnect the vacuum gauge. Test any other hoses by repeating steps 1 through 3, only detaching the gauge when the car is off. When finished, remove the vacuum gauge and reattach any hoses or vacuum sources you disconnected.

Tips and warnings

  • The vacuum gauge can also be used for more advanced diagnostics, troubleshooting and tuning, but this typically requires mechanic-level car knowledge. For tips and info on some of these advanced methods and uses, see the Resources.

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