Iron golems rust in multiple stages, like iron items, rather than all at once. Each stage cuts its maximum HP by 20 (so a rusty golem has 60 max HP, etc.) Applying a can of grease will remove the rust and restore its max HP to normal, and may prevent further water damage for a little while. The golem may also quaff a potion of oil, which has a similar effect, except it also restores current HP as well as maximum by the amount of erosion removed.

Iron golems that rust to death may rarely leave behind a statue (ideally made of iron material) which is implied to be its rusted husk.