When a cylinder head is removed it is a good idea to check it for cracks. There are 3 common methods for doing this. One method is magnafluxing, where a magnet attached to the head and metal powder is sprayed onto the head. Magnafluxing only works with cast iron heads. None of the cars we work on have cast iron heads, so we do not do magnafluxing here. Another method is pressure testing. To pressure test a head, all the coolant passages are blocked off and air is injected into the water jacket. The head is then submerged in water. Air bubbles can be seen coming from the crack. We do not have a pressure tester here because they are very expensive and we do not do enough head repair volume to justify the expense. When we feel a pressure test is necessary, we sublet pressure testing to a machine shop we trust. The third method for crack checking a head is the penetrant dye method. This method is outlined below.
The most important part of crack checking a head using the penetrant dye method is the cleaning of the head. The combustion chambers must have all of the carbon removed. A coating of carbon can hide a crack. The head below has been cleaned. The valves were also removed but this is not necessary for the dye check.
Next the head is sprayed with the dye. The dye is left to sit for about 5 minutes. This allows the dye to soak in to any cracks.
Next the dye is wiped off using a clean rag.
The final step is spraying on a light coat of developer. Any cracks will show up as bright red lines. This one is OK.