coolant

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Sat 15 Dec 2001 10:11
coolant - richard price
I realise coolant expands when hot, does it contract much when the air temperature outside of the car is say +4c to -2c. Many thanks.
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Sat 15 Dec 2001 15:48
Re: coolant - John S
Richard

Most liquids have a relatively low coefficient of expansion. Water expands by about 4% in volume between 0C and 100C. I can't find any data, but I'd be surprised if anti freeze is much different. Thermal expansion is a completely reversible process. So when you say 'does it contract much at say 4C to -2C', the answer is that at around 0C it is about 96% of the volume at operating temperature.

You've picked some interesting temperatures if the question is 'does it contract much between a range of 4C to -2C' though. Water actually has a maximum density at 4C, so actually expands as temperature drops between 4C and 0C, and I believe, if it has anti freeze, will then contract below 0C. Above 4C it reverts to expected expansion as the temperature rises. Below 0C pure water is normally ice, so I don't have data, but the phase change from liquid to solid gives a significant expansion which is what cracks engine blocks.

Between 4C and 0C water contracts by 0.013%, which would not be significant in terms of level of coolant.

Hope this answers the question!

regards

JS
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Sat 15 Dec 2001 16:03
Re: coolant - Guy Lacey
Exactly! That's why ice floats on water when any GCSE student would tell you it should sink. All to do with intermolecular hydrogen bonding don't you know.
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Mon 17 Dec 2001 09:56
Re: frozen ponds - John S
Guy

The fact max. density occurs at 4C is also the reason why ice forms from the top downwards, and the bottom of the pond is at 4C. Goldfish are very grateful!

regards

JS
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Sat 15 Dec 2001 20:47
Re: coolant - alvin booth
John,
That was excellent and bought some memories back. Yes water is of course at its max densityat 39f in old measurement and has always been one of those "I wonder why" theories to myself.
In practical terms Richards query would be very minimal when you consider that the effect on an unpressurised heating system is simply taken care of by setting the water level via the ball valve in the make up tank (which may only be around 15gallons) to about a third up the tank. This takes care of all expansion in a large heating system from ambient up to 180f with little rise in level.
Alvin
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