How to Bleed a Radiator: A DIY Guide

January 27, 2012

In maintaining your cooling system, you can both bleed a radiator of excess air, and flush a radiator of old coolant.

Bleeding a Radiator

Bleeding the radiator is the process of releasing the air that may become trapped in the upper portion of a car's radiator. Over time, air finds its way into the overflow tube and reservoir of your radiator system. When this happens, it may create air bubbles that actually block or prevent coolant from passing through hoses and tubes in your cooling system.

3 Methods of Bleeding a Radiator

  • Open the bleeder valves. Some vehicles have a radiator bleeder valve located at the top or front of the radiator. This valve is made specifically for bleeding off air that becomes trapped in the upper portion of the radiator
  • Elevate the car. Simply jacking up the front end of your vehicle lifts your radiator to a point that is higher than the rest of the cooling system. This will help force air pockets closed and dissipate air bubbles into the atmosphere. When elevating your vehicle, make sure that the radiator cap or reservoir tank cap is loose, to help speed the process
  • Start the car with the radiator cap off. One of the easiest ways to bleed your car's radiator is to simply remove the radiator cap and then start your engine. Leave the vehicle running until it reaches its normal operating temperature. It may take between 15 or 20 minutes before your car generates enough heat to push out the air that has been trapped in your car's cooling system. You may find that you need to add additional coolant, as air pockets can artificially inflate coolant levels

    Flushing a Radiator

    Flushing a radiator will not only refresh the coolant, but will help to prolong the life of your radiator by removing dirt and other debris that has built up. It is easy to learn and will take the average person about a half an hour.

    Tools and Materials

    • Fresh coolant
    • A garden hose
    • Pliers
    • A drain pan

    Prep the Radiator
    Put the drain pan in place under the vehicle to catch the old coolant. Remove the cap from the radiator and the drain plug. As soon as the plug is removed, the old coolant will pour out into the pan underneath.

    Flush the Radiator
    Put the garden hose into the top opening of the radiator. Turn the water on and set it to flow lightly. The water will fill the radiator but will flow out of the bottom drain. You can do this with the car off to flush only the radiator or with the car running to flush the whole cooling system. Watch the water coming out of the bottom drain. When you see that it is clean, you will know that the radiator has bled completely. Remove the garden hose and replace the plug.

    Replace the Coolant
    Most manufacturers recommend a mix that consists of 50 percent coolant and 50 percent water until the radiator is full. Once the radiator is full, replace the cap. Fill it slowly to help avoid too much air building up in the radiator. You can also park so that the nose of your car is on a slight incline, higher than the rest of the car. When the coolant is visible in the radiator, start the engine. When the engine warms up and the coolant starts to circulate, slowly add more until it is completely full.

    Fill the Overflow
    Fill the overflow tank, also known as the reservoir tank, with coolant. Keeping the overflow tank full helps to remove air bubbles and also works to ensure that your radiator will always be full.

    Check Your Work
    Drive your car for a while so the engine can warm up. Turn on the heater and allow it to run for a few minutes to ensure that it blows hot air. Stop the car, let it cool back down and the check the fluid level in the radiator one more time. Add more coolant to top it off if necessary.

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