Here is a piece of an article from a previous Chargin Thunder :::
So now you know what a head gasket is and what it does. So why do they fail? Well, here is a list of common causes. Ranked by what I saw at the shop.
Overheating. By far the most common. Could be as simple as a defective $5 thermostat or a plugged radiator, but run the motor hot and bad things happen.
Detonation. This could be a result of low octane fuel, carbon buildup, too much ignition timing, or overheating. A combination of these will produce failures in a hurry. In the combustion chamber, the only thing that keeps the pistons from melting is a small layer of gas that "clings" to the piston dome. Detonation sends a shockwave and flame spike through the cylinder that rips this layer away exposing the actual metal surface to the combustion temperatures. My head gaskets failed from detonation. The detonation actually split the fire ring. Severe detonation can burn holes through pistons too.