Question on thermal equilibrium?

So I'm not too sure about the answer to this question: explain why it is advisable to add water to an overheated automobile engine only slowly, and only with the engine running?

So if something is overheating, it makes sense to want to cool it. Since the water's temperature is less than that of the engine, pouring it on will lower the temperature of the engine. But what about thermal equilibrium, and engines in particular, makes it risky to pour in water quickly? Will too much water mean that the liquid will hit the engine without being boiled, thus damaging the engine? And what about an engine running makes it advisable? Is it because it keeps its overheating temperature constant?

 

Yeah, this was a difficult question to think about, because I'm not sure if an understanding of engines was needed or not. If I had to pick an answer it would be that the water needs to be boiled first, and too much water means only some of the water is boiled whereas the rest of the water can damage the engine. However, since I'm ignorant when it comes to car engines (thermal equilibrium too) I'm not sure if THIS is the particular reason why it's wise to pour the water slowly. I know that this forum doesn't concern itself with automobiles, so I'm guessing that the question itself shouldn't need an understanding. Without it being boiled, the liquid may hit other parts of the engine NOT overheating, and thus shrink the parts of the engine. The shrinking will cause a damage to the engine.

 

Well, if the engine is off the engine will slowly but surely cool down. But maybe not evenly. Adding water when it's at its hot state gives a more even distribution of equilibrium, so the engine won't break off.