I am in the process of installing a new engine on my Ford 850. My old block was bad and I found a replacement. I just got it back from the machine shop and noticed something. The replacement block has a "circle" on the block surface that is not found on my old block. It goes into the water jacket near where the water pump mounts. There is no corresponding hole in the head or in the head gasket for it either. See the pictures below. Does anybody know what it s for? I scanned a few pictures online and noticed some blocks have it and some blocks don t. Is this something I need to be worried about? This is my go to site for information and I figure somebody here will have some insight.