Can a cracked head gasket on a 1997 BMW 528i be responsible for sporadic overheating or is it always a side effect of another overheating problem?

In general, a cracked head, a failed head gasket, a cracked block (water jacket) or something similar isn't somehthing that will cause "sporadic overheating" or the like. When failures of this nature occur, they almost invariably cause overheating every time the vehicle is run for more than a few minutes. The problem doesn't "surface now and then" to bug a car owner. It presents itself and stays around until it's taken care of. And if it is ignored, it gets worse, and more damage can occur. But you knew that. There are some checks to determine if a gasket has failed, and some good advice on this already exists elsewhere in WikiAnswers. A link is provided to one. Good luck.