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The Freezing of Water

By Norman Nock

Originally published in the Austin-Healey Magazine, January 1997

Crystal Bay, Lake Tahoe, 22-23 December 1996: The traffic on the road has not moved in six hours so I could not go skiing. It seemed to be the ideal time to write about the freezing of water, and cold-weather driving.

The Swedish astronomer, Anders Celsius, first established a thermometer scale in 1742. He made the boiling point of pure water to be 0°. Then he worked backwards to a freezing point of 100°. These values soon changed to 0°C freezing and 100°C boiling. Fahrenheit set the freezing point for salt water at 0°F, and set body temperature at 96°. This is why 32° (freezing) and 212° (boiling) are arbitrary numbers.

The abnormal expansion of water

If you fill a capillary tube with water, place it in your freezer in an uncapped vertical position, the contraction of water will be noticed by a drop in the water level. As the temperature falls still lower, the level in the tube actually rises. Water unlike other liquids, will contract until 39°

F (4°C). As the temperature goes lower still it then expands until it reaches the freezing point. This is why ice will show itself in the top of the radiator first. The water below 39°F (4°C) is now lighter and it rises to the surface – which is why a lake freezes on the surface. When the water has turned to ice it expands still further. The pressure that results from freezing can be visualized by placing a plastic bottle full of water in the freezer. The bottle will expand and can split open. (I just finished cleaning up the refrigerator – a can of coke froze and split open – ed.)

If you park your car outside when temperatures fall below freezing and you have pure water in your radiator, the water will freeze just like the water in the plastic bottle, expanding as it does so. The damage that results – like a cracked block – can be very expensive.

When I was a young boy in the late ‘30s, I remember my father would drain out the cooling system so it would not freeze and crack the engine block. Heaters did not come with the cars then so it was not necessary to empty a heater core.

The freezing point of your coolant with antifreeze can be checked by its specific gravity using a hydrometer. When antifreeze is added to water you make it heavier than water. The hydrometer will measure how much heavier it is, and the scale will show the freezing point of the antifreeze/water solution you are measuring. If the quantity of antifreeze is not sufficient you can still freeze up the car. For example, if you’re driving a car in very cold weather (-30°

F) the water passing through the radiator could cool to the point of sludging and freezing the coolant in the radiator, causing overheating and other problems.

However, the saying “if one is good, two is twice as good” does not hold for antifreeze. Put another way, if you think you will get more protection if you use 100 percent antifreeze, forget it. If you use pure antifreeze, you will be protected from freezing, but without any water in the antifreeze, not all the engine heat will be carried away since water has more capabilities in the regard. Minimum protection is a 50 – 50 mix of antifreeze and water. For best results, use a mix of 70 percent antifreeze and 30 percent water. That will protect your engine to -84°F, and will provide a boil-overprotection of 248°F with a 7-lb. cap. An antifreeze solution will expand more than water when heated (approximately 1/3 pint per gallon). To avoid loss of coolant due to expansion, don’t fill your radiator completely. The coolant level should be just below the radiator cap when the engine is warmed up, or about 1-inch below the cap when the engine is cold. There is virtually no loss of ethylene glycol antifreeze due to evaporation. Any evaporative loss would be water.

The same considerations that apply to water in the radiator during cold water also applies to the water in the batteries. When you have a fully charged battery, the acid/water combination will start to freeze at about -90°F, at which point the liquid will begin to turn to sludge. It the battery is only half charged, however, the acid/water combination will begin to freeze at 0°

F, at which point the case will crack and acid will spill out. If the battery has zero charge, the water will freeze at 32°F.

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