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Question on thermal equilibrium?

  1. Jan 8, 2015 #1
    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?
     
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  3. Jan 8, 2015 #2

    Bystander

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    The way the forum works, is that you have to commit to an answer/approach. Pick something, and defend it.
    You're fishing. It's close, so try developing the idea a bit. "Damage how?"
    More fishing. Develop the idea.
     
  4. Jan 8, 2015 #3
    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.
     
  5. Jan 8, 2015 #4

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    Bingo. Just like baking marbles on a cookie sheet and dropping them into water to make fractured marbles for interior decoration --- or, you're too young, and Ralph Nader forbade your mother from doing that? "Temperature shock." Great.

    Now, why keep the engine running (which keeps the water pump running) as you add water slowly?
     
  6. Jan 8, 2015 #5
    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.
     
  7. Jan 8, 2015 #6

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    Coolant is circulated through the engine by the "water pump" (little water and a lot of ethylene glycol), and lowering the coolant's temperature by gradual addition of water prevents large temperature differences being produced in the block or heads that might crack those pieces. Almost guaranteed to happen if you turn cold water on a dry hot engine.
     
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