While installing the oil pressure gauge in my 53K, I noted another tapped hole about halfway between the gauge and the pressure relief valve. Goes well into the block. Couldn't recall any such, and didn't see anything in the manuals indicating anything there. I have some vague recollect of a second block drain plug, but see no reference to any. What could it be? Suppose I could just plug it before starting, but I like to know what things are.
