# Engines: Antifreeze leaks, while plain water does not. Why?

**URL:** <https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754>\
**Category:** Factual Questions\
**Created:** [November 24, 2009, 9:44am UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754 "2009-11-24T09:44:13Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Deereman](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@Deereman](https://boards.straightdope.com/u/Deereman)\
**Post date:** [November 24, 2009, 9:44am UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754/1 "2009-11-24T09:44:13Z")

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This is something I’ve heard about, and also had happen to me a few times now…

Take an old engine (or new rebuilt) and if the coolant system is filled with plain water, everything’s fine, no leaks, drips, nothing.

But fill the engine with antifreeze, and you’ll find every little drip and dribble, bad radiator core, or cracked block. OK, I’m exaggerating, but to sum it up, why (if there’s something not sealed completely right) does antifreeze leak, where water does not?

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**Author:** ![Deereman](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@Deereman](https://boards.straightdope.com/u/Deereman)\
**Post date:** [November 24, 2009, 10:17am UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754/2 "2009-11-24T10:17:29Z")

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Oh, I have a guess that it has to do with surface tension, but I’m not really sure.

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**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\
**Post date:** [November 24, 2009, 11:40am UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754/3 "2009-11-24T11:40:20Z")

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Perhaps the water is also leaking but evaporating, whereas the antifreeze (better called engine coolant) does not evaporate as readily. Since it is ‘brightly’ dyed you can see where it has leaked - you notice it better.

The reason the engine coolant does not evaporate as easily as straight water is because the vapour pressure is lowered by the additives. Vapour pressure reflects the volatility of a substance - higher vapour pressure --\> more volatile. Additives in the engine coolant are not just to reduce the freezing point, but to increase the boiling point (r. educe vapour pressure).

My WAG

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**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\
**Post date:** [November 24, 2009, 12:39pm UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754/4 "2009-11-24T12:39:28Z")

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antechinus hit it on the head. Also, the hotter the water, the faster it evaporates.

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**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\
**Post date:** [November 24, 2009, 2:58pm UTC](https://boards.straightdope.com/t/engines-antifreeze-leaks-while-plain-water-does-not-why/518754/5 "2009-11-24T14:58:04Z")

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> [@racer72](#):
>
> antechinus hit it on the head. Also, the hotter the water, the faster it evaporates.

That is part of the problem. Antifreeze is also used as an anti scale. So soft deposits of scale can be loosened and readsorbed into the solution. Just plane water will cause scale and corrision deposits helping to form a plug around a small pin hole.