Automotive freeze plugs are round metal plugs installed in the casting holes in engine blocks. These plugs are thin and sometimes rust through, allowing engine coolant to leak. When this happens, the old freeze plug must be removed and replaced with a new one. The installation of engine block heaters also requires the removal of a freeze plug. The problem is, these plugs are pressed in and are recessed in the block.
Many automotive mechanics simply use a hammer and punch to drive the old plug through the casting hole and into the block. They then turn the plug 90 degrees so that it can be grasped with pliers and pulled from the hole. This works most of the time, but on occasion will fall into the cooling passages and be impossible to retrieve. While not the best outcome, it isn't a major problem to leave it in place if it absolutely cannot be retrieved.
When access allows, the best method to remove a freeze plug is to pull it from the casting hole. A dent puller or slide hammer with a screw point is screwed in a pre-drilled hole in the freeze plug and used to remove the plug. A possible problem with this method occurs when the plug has rusted to be very thin and the screw simply pulls from the metal. For this reason, it is best to drill the hole near the outer edge of the freeze plug where the metal is likely to be strongest.
The third method to remove a freeze plug is to drill a larger hole in the plug and insert a screwdriver point in the hole. Using the edge of the casting hole as a fulcrum, the mechanic simply pries the freeze plug out of the hole. If the center of the plug has rusted through, drilling the hole isn't necessary and the screwdriver is inserted directly through the freeze plug.
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