Core Plugs, Welch Plugs and Freeze Plugs are what we call the plugs in the side of our engines, these plugs have nothing to do with freeze protection. These openings in the water passage are there to allow the sand from the casting process a place to exit. After the block is cast it goes onto a shaker that shakes it hard enough to break the sand out of the internal passages via these plug openings. After the sand is all out the plug is installed to seal the opening. If your block was to freeze it would break all the way at the bottom of the water jacket way before it would ever pop the plugs...
Mike B
