Cracked engine blocks are almost always caused by an overheating engine, or in rare cases, a casting failure. However, overheating is often the symptom of an underlying issue. Excess heat can be caused by low coolant, water pump failure or overpowering.
The most common cause of an overheated engine is low coolant levels. The coolant in the vehicle only cools the area through which it runs, and when there is not enough coolant in the system, certain parts of the engine are prone to overheating. Another possible root cause is the failure of the water pump system. The water pump is what powers the coolant through the system and without it the coolant will not get to where it needs to go. Also, when an after-market supercharger or turbocharger is added to an engine, the additional power generated can lead to a level of heat that the original engine was not designed to handle. This could cause a critical failure of the engine block if it gets too hot. One rare cause of a cracked engine block is casting failure. This involves a defect in the manufacturing of the engine mold, leaving the metal thinner than it should be in some places, and these weaker areas could crack over time under the stress of operation.