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During studying engine's exhaust as I asked here, I have to go far. The thing I though is quite simple, the fact is complicated. Thence I knew that there is water produced in combustion process. The combustion formula is: $C_8H_{18}+12.5O_2\rightarrow8CO_2+9H_2O$. Mean, every 1 of 4 strokes of 4-strokes engine will produce water (cyclic process: intake-compress-power-exhaust). This is the answer for me why the muffler always tear-dropping water especially in the morning or when the weather is cold.

But, that happened if the car is still good enough. Before my current car, my old car seems didn't have that kind of tear-drop water from the muffler. Not sure what had happened to the engine. The muffler was dry and clean, no smoke. So my question is, where the water have gone? Which one is better, a car with water tear-dropping from the muffler? Or a car without that water? My question is for the same ca or closed in it piston's displacement and its power.

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  • $\begingroup$ Your combustion formula is incorrect- there are other products of combustion... $\endgroup$
    – Solar Mike
    Commented Nov 17, 2018 at 5:29
  • $\begingroup$ What is the correct formula? Is the correct one still producing water? $\endgroup$
    – AirCraft Lover
    Commented Nov 17, 2018 at 10:51
  • $\begingroup$ Well, what about unburnt hydrocarbons? $\endgroup$
    – Solar Mike
    Commented Nov 17, 2018 at 11:13
  • $\begingroup$ Is your new car more efficient than your old one? Less burned fuel means less water... $\endgroup$
    – hazzey ♦
    Commented Nov 17, 2018 at 14:37
  • $\begingroup$ Yes, of course. The newer is more efficient. Both are the same brand, Toyota. But the old one is still carburetor while the new one is fuel injection. But however, the chemical reaction inside the combustion chamber are same. $\endgroup$
    – AirCraft Lover
    Commented Nov 18, 2018 at 1:21

2 Answers 2

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Anytime your car's engine is running, it is producing water vapor which leaves the engine through the exhaust system.

When the engine has just been started and the exhaust system in your car is cold, the water vapor in the exhaust condenses into liquid water and trickles out the tailpipe.

When the engine has been running for a while and the exhaust system is hot, the water vapor remains vapor as it flows out the pipes and exits the tailpipe as invisible vapor.

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  • $\begingroup$ Quote: "When the engine has been running for a while and the exhaust system is hot, the water vapor remains vapor as it flows out the pipes and exits the tailpipe as invisible vapor." I agree with this. But what I am asking, of course for the same situation, when time is morning and cold. Where the water have gone whereas no in the muffler? $\endgroup$
    – AirCraft Lover
    Commented Nov 17, 2018 at 10:51
  • $\begingroup$ So, you should edit your question to make it clearer... @AirCraftLover $\endgroup$
    – Solar Mike
    Commented Nov 17, 2018 at 11:14
  • $\begingroup$ as I pointed out in my answer, when time is morning and engine is cold, the water vapor coming out of the engine changes into liquid water inside the cold exhaust pipes and runs out the tailpipe as a thin stream of water. $\endgroup$
    – niels nielsen
    Commented Nov 17, 2018 at 17:21
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I think the answer to what you are asking is that, normally the water form combustion is produced as a gas as, inevitably it is at a temperature well above the boiling point of water.

While it is a gas it is invisible and you will only see it as drops of liquid is it cools down enough to condense. whether or not this occurs depends on a variety of factors including the weather conditions, the layout of the exhaust and how hot the exhaust gases are when they enter the exhaust system.

A lot of modern cars need to run the exhausts fairly hot in order for catalytic converters and particle filters to work properly and will often adjust the air/fuel ratio to ensure that the exhaust heats up quickly.

On possible difference between cars is where the catalytic converter is located. Being a fiarly hot component they need to be puts somewhere away from anything heat sensitive

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  • $\begingroup$ Seem like it is flipped. If the reason is as you said that lot of modern cars need to run the exhausts fairly hot in order for catalytic converters and particle filters to work properly and will often adjust the air/fuel ratio to ensure that the exhaust heats up quickly, that probably reasonable if my case is my newer car didn't produce water whereas the older one produced. But the actual is, there is water from the muffler with my new car and no with my old car. $\endgroup$
    – AirCraft Lover
    Commented Nov 18, 2018 at 5:44

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