Hi, I searched on here and Google and cannot find what the hole in the picture is for and why it is directly connected to a coolant passage. It leaks coolant once you fill it up to that level and if you blow air in it you can hear it in the radiator. It seams to be threaded but the head doesn't give it a seating surface if it were a gasket-ed plug or something. Maybe it is a taper thread. Inside the hole you can see the head bolt. So the hole is cross drilled right into the head bolt hole on the head. It seams very intentional so I don't think it is a weird rust hole which seams unlikely. BTW, this is a complete engine freshen up and when I had the head off and was cleaning it, I noticed this hole and it was filled with crud that I was able to chip away at until clear. This should have been a clue to investigate what it was for when I had it apart but I didn't.
Any ideas. This is located right behind the coil.
Any ideas. This is located right behind the coil.