The next step is to inspect the block thoroughly for cracks in the casting. These may be caused by overheating, freezing, or stress from severe-duty usage. The prescribed method is called Magnafluxing. The Magnaflux machine uses an application-specific, high-powered electromagnet placed on the engine block. With a strong magnetic field induced, a colored iron powder is sprinkled around the area between the poles of the magnet. If a crack is present, the iron powder will enter it and identify its outline. A crack was found in this block during the Magnaflux process. It is represented as the long line seen just above the lifter valley in the photo.