Help! Small block 360 has a knocking sound

Ok guys, I just fired it up and got temperature readings off of all the cylinders, and cylinder 5 was a bit lower than the others. with the engine running, cylinder 5 was at about 300 to 350 degrees, while the other 7 cylinders were at about 400 to 450. I don't think number 5 is a dead cylinder, but something is definitely up with it.