2 things: Will not get hot enough to burn water, ever. That temp is about as high as the melt point for most steel and Iron. 100c is the point where water vapor forms, not molecular separation. You see that in Magnesium fires, about 1900c. Second, thermal expansion takes energy, heat energy. When the cold water turns to steam, is is taking heat engery with it as it does so.
Per Andrews post, its possible to get around that. I know it is, I just dont know how, and I'll refer back to steam engines. Back in the days of steam locomotives, some used a horizontal piston powered entirely by steam. They managed to get it to work, I'm sure we can do it today.
So, simply, water turning to steam uses heat energy, and therefore dissipates heat. Though I doubt its enough to cool a big engine.