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Should you factor in wind chill when pouring antifreeze?

Published January 14, 2013


Eric Lai answers readers’ auto questions every week for Wheels.

Q: Do I have to factor in wind chill when determining the correct antifreeze mix ratio for my car?

A: “Wind chill” is a theoretical estimate of how cold the outdoor air temperature “feels” on exposed skin depending on factors such as humidity and air velocity.

Inanimate objects like automobile engines will not chill to below the actual outside temperature. For example, if the ambient outdoor temperature is -10 Celsius, with a wind chill of -30 C, your engine will not get colder than -10 C, irrespective of the wind chill.

Once an engine is started and begins to warm, the amount of airflow around it affects its rate of cooling. That is, an engine will cool faster with a higher wind chill factor (i.e. stronger winds) than if there was no wind but will not drop below the actual outdoor temperature.

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Likewise, your outdoor home thermometer will only indicate the actual temperature, never the “wind chill” temperature. But note that if the thermostat is in direct sunlight, it may read around 4-7 degrees higher than the ambient air temperature due to the thermometer itself being warmed by the sun.

As for antifreeze, a 50/50 mix providing freeze-up protection down to -37 C is generally optimal for southern Ontario. In far Northern regions, the mixture ratio can be increased up to a maximum of 70/30 (antifreeze/water) to provide protection down to -58 C. However, this decreases the ability of the fluid mixture to absorb heat and the system could overheat in less severe temperatures.

Now, if you think filling your vehicle entirely with pure coolant would provide the highest freeze-up protection, think again. With no water mixed in, pure antifreeze will freeze at only -12 C (+10 F).

Automotive coolant is toxic. Old fluid should be disposed of at a toxic waste facility (check with your local municipality for information). Flush away any driveway puddles with a garden hose to prevent accidental poisoning of children, pets, or wild animals.

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