If there is a suspected crack in a cylinder head, it is sometimes possible to repair these and we have many different techniques that can work.
First identifying the crack (cast iron) we use a magnetic particle penetrant under a special fluorescent light to establish if the repair is viable. If so then there are several different ways to rectify including welding.

Aluminum crack testing is achieved with dye penetrant system or in the case of cylinder heads and oil coolers pressure testing.