Recently I was involved in a discussion on Monte Cook's boards about which was tougher, an iron golem
or an iron statue the size of an iron golem, the question came up of
whether the golem was solid iron or hollow.
Short answer: An iron golem is not solid.
5,000 lbs of iron = 2,270 kilograms of iron.
2,270 kilograms of iron = .288 cubic meters of iron (iron's density is 7,874 kg/cu meter) or approximately .3 cubic meters of iron.
An iron golem is "twice the height of a human," and we can assume that if it's proportional then it's twice the width and depth as well, and therefore has eight times the body volume of a human (1 human x2 height x2 width x2 depth = x8).
One human has a body volume of approximately 3 cubic feet, which is approximately 1/9 of a cubic yard (27 cubic feet, which for our purposes is essentially the same as a cubic meter). So eight humans is about 8/9 of a cubic meter, or approximately 1 cubic meter.
If an iron golem's body fills a volume of 1 cubic meter and 5,000 pounds of iron only takes up .3 cubic meters of space, then an iron golem (which is made of 5,000 pounds of iron) has to be hollow, for the remaining .7 cubic meters of space that its body fills must be full of air (or marshmallows, or whatever).
FYI, .3 cubic meters of iron is roughly 9 cubic feet of iron, and if a human is 3 cubic feet then 9 cubic feet of iron is enough to make a solid iron statue about 1.45 times the size of a human in all three dimensions, or a figure 8.7 feet tall, which is just shorter than the shortest adult ogre.