How to Bleed a Cooling System With Trapped Air

Written by mike aguilar
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How to Bleed a Cooling System With Trapped Air
Bleeding is an essential radiator service. (radiator humour image by John Sfondilias from Fotolia.com)

Whenever you drain and refill the cooling system for any reason, you're more than likely to have small pockets, or bubbles of air trapped in the system. These air bubbles can create problems. The process of removing air from the cooling system is known as "bleeding" the cooling system. The exact process differs by make and model, but the basic process is the same for all cars.

Skill level:
Easy

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Things you need

  • Socket
  • Universal swivel adaptor
  • Extension
  • Ratchet
  • Flat-blade screwdriver
  • Fresh coolant

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Instructions

  1. 1

    Remove the radiator cap by turning it counterclockwise while pushing down. Verify that the coolant level is just below the filler neck.

  2. 2

    Start the engine. Turn the heater control to full hot, leaving the fan on "off" or "low." Allow the engine to heat to operating temperature.

  3. 3

    Open the bleeder valve on the thermostat housing by turning it counterclockwise with a ratchet and socket. Keep the valve open until no more air bubbles escape and a steady stream of coolant flows out. Close the valve by turning it clockwise with the ratchet and socket.

  4. 4

    Allow the cooling fans to cycle on and off once and verify the coolant level in the radiator and overflow bottles and refill as needed.

  5. 5

    Verify that all hose clamps are tight by turning the worm screws on the clamps clockwise with a screwdriver.

Tips and warnings

  • Park the car on an incline with the front end higher. Gravity will help force the air trapped in the system to the highest point, the radiator cap or bleeder valve. Ramps or a jack and jack stands can also be used to raise the front end.
  • A small hole (1/8 inch or smaller) can be drilled in the flange of the thermostat to allow trapped air to flow out of the system quicker.
  • Use caution when opening a cooling system, as coolant under pressure may escape.

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