How To Replace Rusted Freeze Plugs

A freeze plug is a metallic disc that fills in the sand casting holes created in the cooling systems of the internal combustion engines. These holes are actually left in the casting for the removal of the sand particles when the casting has cooled. A freeze plug or a welch plug is a thin, dome shaped disc of some ferrous metal which is used to stop water from crossing over these cavities. Due to their contact with water at all times, freeze plugs get corroded easily. The plugs then demand a replacement; however, that depends on the ease of accessibility. In some engines freeze plugs may be very hard to reach while in some, it is easy to trace and replace them.

The purpose of the freeze plug is to protect the engine against the freeze damage. In cold weather, water turns into ice and expands. If there is not enough anti freeze agent present in the coolant the fluid can freeze and cause damage to the engine. So it is advised to inspect freeze plugs from time to time.


  • 1

    First of all trace the freeze plug that has corroded and is causing leakage. Use a jack to lift your vehicle and add water in the radiator (simple clean water, no need to use coolant at this stage). Lay down under the car to find out where the water is dripping from the car. If you cannot locate it with your bare hands use a tissue paper to locate the leaking plug. You should also use a torch if the plugs are not clearly visible.

  • 2

    After locking on to which plug is leaking, drain the contents of the entire cooling system. Open the screw under the radiator and give it 4-5 minutes to drain completely. Now the plug that was previously leaking will stop dripping. Use a dremmel to0l and place the required bit on the plug. Don’t use excessive force as it may cut through the entire engine block. If the cut line is visible, use a screw driver to fit in the cut and rotate it to open the plug. Use pliers to grab the freeze plug and take it out of the engine block.

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  • 3

    Replace the new plug in the place and tap it with a hammer to align it exactly in the same place as the previous plug. After locking in the freeze plug fill in the cooling system with a coolant or water and double-check for leakage.

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