How to Tell if a Radiator Cap is Bad?

Written by gregory crews
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To maintain your radiator, you will need to test the pressure on the radiator as well as on the cap. The coolant system of your vehicle relies on pressure to properly circulate air in your vehicle to keep it cold. The pressure tester can be purchased at your local automotive parts store, or you can also borrow one. Most parts stores have a lease program, so you do not have to spend a lot of money on a one-time project.

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Things you need

  • Radiator pressure tester
  • Radiator pressure cap adaptor

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    Testing the Radiator Cap

  1. 1

    Inspect the radiator cap for visual defects. Look for broken seals and push the spring on the bottom of the cap in. The spring should bounce back.

  2. 2

    Moisten the seal on the cap with water. This will help it to seal during testing.

  3. 3

    Install the radiator cap on the pressure tester adaptor. The cap will screw on like it would into the radiator.

  4. 4

    Install the cap and the adaptor to the tester. They will attach as they would into the radiator.

  5. 5

    Pump the tester to the recommended pounds indicated on the cap. You can pump higher than the indicated amount printed on the cap, and the pressure will release until it gets to the recommended pressure that is stamped on the cap.

  6. 6

    Replace the cap if the cap does not hold pressure at or below the recommended amount.

Tips and warnings

  • You can use the pressure tester to test your radiator for leaks. You will need to remove the adaptor to test the radiator.
  • Do not test the coolant system until the vehicle is cold. The heat from the coolant and the pressure could result in burns.

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