A crack in an engine block can have disastrous consequences, but the cracks can be challenging to locate with the naked eye. Even a small crack has the potential to allow fluid leaks, depending on its location, and cracks usually spread over time. "Magnafluxing" is the process of using iron oxide particles and a magnetic field to locate cracks on an iron engine block. This technique is ineffective on aluminum, however, so the Magnaflux Corporation offers penetrating dyes that accomplish the same task on aluminum.
Place the aluminum piece or block on a board outside so the penetrating dyes don't stain or damage any other components or materials.
Clean the block thoroughly with a rag and a mild degreaser or engine cleaner to give you a better view of the aluminum without dirt, grease or debris interfering.
Spray the aluminum with a canister of Spotcheck nondestructive testing material (Spotcheck SKC-S.) This is designed to help clean the block and prepare it for dye inspection without causing harm to the components. Spotcheck is the Magnaflux brand for dye penetration.
Wipe the material off of the aluminum with a clean rag, then let the remaining residue dry for the next 15 minutes.
Apply the Spotcheck dye penetrant (Spotcheck SKL-SP2) to the aluminum so it's completely covered, then let it dry for another 15 minutes.
Wipe down the aluminum with another clean rag to remove any excess penetrant once the coat has mostly dried. Spray a clean rag with the nondestructive testing material and wipe down the aluminum again with the treated rag.
Use a can of Spotcheck developer (Spotcheck SKD-S2) on the aluminum. Once the aluminum has been fully covered, any crack in the material should appear as a bright red dot or line as a result of the earlier penetrating dye. If you don't see any red marks, the aluminum should be crack-free.