Freeze plugs are metal --- either brass or steel --- and rust in the block, especially if the vehicle owner uses straight water in the radiator, instead of antifreeze. Removing a freeze plug is difficult enough, and a freeze plug rusted to the block makes it more difficult to remove. If you do not replace a rusted through freeze plug, the coolant will leak and the vehicle will overheat. If the hole is big enough, it may take only a few minutes for the water to drain out and the engine to overheat.
Spray the freeze plug where it contacts the block with rust penetrant. Allow it to soak for 15 to 20 minutes.
Place the screwdriver near the edge of the inside of the freeze plug. Tap the screwdriver with a hammer just enough to loosen the freeze plug from the block. Take care to not knock it hard enough to push the freeze plug into the block. Grab the edge of the freeze plug with the pliers and pull it out.
Drill a hole in the center of the freeze block if you cannot pull it out. Stick the screwdriver into the hole and pry the center of the freeze plug toward you. The freeze plug may pull out. If not, you may be able to pry enough of the center out to grab it with the pliers to pull it out.
Soak the freeze plug with rust penetrant again, and let it soak in for another 15 to 20 minutes. Repeat the entire process to try to pry or pull the freeze plug out of the block.
