[Abathar]

My grandmother cracked an engine block once years ago by spraying it with cold water after it overheated to cool it off.

Seems a lot of people would kind like to understand the answer to the question you proposed.

[Ancesthntr]

My grandmother cracked an engine block once years ago by spraying it with cold water after it overheated to cool it off.

I'll bet that gramps was really pleased about that.

[expatpat]

We're talking about 2 different things. The cracked block et al are due the water cooling only one part of the block, which sets up large stresses from differential thermal expansion/contraction.

The boiler issue, OTOH, is due to the expansion of water when it undergoes a phase change from liquid to vapor -- pipes bursting due to freezing in the winter is much the same thing, except that here the phase transition is to the solid state.