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  • Writer's pictureJJ Johnson

What is Coolant & Why Does it Matter?


I was recently asked about what coolant is and how it affects the function of the heater in your vehicle. Most people only hear about their coolant, or antifreeze, when they are asked if they want to have it topped off while they are having the oil changed. But what is antifreeze?


Antifreeze, is a fluid that runs through the engine of your vehicle to help dissipate the heat generated by combustion and keep the engine from overheating. Antifreeze is heated as it runs through the engine. It then runs out of the engine and into the radiator at the front of the vehicle. As the cool air flows through the radiator, it cools the antifreeze down before it is cycled back into the engine to begin the process over again. The heater on your vehicle uses the same principal. The hot coolant runs through the heater core, which functions like the radiator. The cold air is heated as it runs over the coils of the heater core that have hot coolant running through them. That hot air is then pumped into the cabin which heats the inside of your vehicle.


Why not just use water? Water has a freezing point of 32 °F. If we put plain water in our engines in colder climates, it would freeze in the small coolant passages of the engine causing it to expand and destroy the engine. Antifreeze is used to lower the freezing point, which allows it to be used even in cold climates. Water also has a boiling point of 212 °F. An engine has a normal operating temperature of 195-220 °F. If we used regular water, it could boil under normal engine operation which would limit its ability to take heat away from the engine, and would subsequently cause the engine to overheat. Antifreeze has a higher boiling point as well, which allows the engine to operate safely, even in extreme heat. A 50/50 mix of antifreeze and water gives freezing protection down close to -35 °F and a boiling point close to 223 °F. It is important to have the proper type and mixture of coolant to ensure safe operation in the extreme temperature ranges that your vehicle can be subjected to.


Finally, if your coolant is low, then the heat can’t be transferred away from the engine, which can cause it to overheat. Modern engines are often cast out of aluminum to save weight and increase fuel efficiency. However, that means that they are extremely susceptible to warping in high temperatures. If an engine warps it will no longer run properly and will need to be replaced. It is not uncommon for engine replacement to be close to $20,000. That is why it is crucially important to keep your coolant at the correct level.

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