Fluid
Cars operate in a wide variety of
temperatures, from well below freezing to well over 100 F (38 C). So whatever
fluid is used to cool the engine has to have a very low
freezing point, a high boiling point, and it has to have the capacity to hold a
lot of heat.
Water is one of the most effective fluids for
holding heat, but water freezes at too high a temperature to be used in car
engines. The fluid that most cars use is a mixture of water and ethylene glycol
(C2H6O2), also known as antifreeze. By adding ethylene glycol to water,
the boiling and freezing points are improved significantly
.
.
Fluid - Freezing Point
- Boiling Point
·
Pure Water: 0 C / 32 F
- 100 C / 212 F
·
50/50 mix of C2H6O2/Water: -37 C / -35 F
- 106 C / 223 F
·
70/30 mix of C2H6O2/Water: -55 C / -67 F
- 113 C / 235 F
The temperature of the coolant can sometimes
reach 250 to 275 F (121 to 135 C). Even with ethylene glycol added, these
temperatures would boil the coolant, so something additional must be done to
raise its boiling point.
The cooling system uses pressure to further raise the boiling point of the
coolant. Just as the boiling temperature of water is higher in a pressure
cooker, the boiling temperature of coolant is higher if you pressurize the
system. Most cars have a pressure limit of 14 to 15 pounds per square inch
(psi), which raises the boiling point another 45 F (25 C) so the coolant can
withstand the high temperatures.
Antifreeze also contains additives to resist corrosion.
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