How do engine coolants work?
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The basic function of a coolant is to take heat from where it is to somewhere else. In the case of a car, that means taking the heat out of the engine block. Of course, the heat still has to go *somewhere*, and it can’t just keep going into the coolant because that coolant will get super hot, and then it can’t carry heat anymore.
So, the coolant carries the heat to a radiator. The radiator exchanges the heat with the air. The engine can also directly exchange heat with the air, but it isn’t very good at it. The engine block is a pretty big, solid chunk of metal. To efficiently exchange heat you need a lot of surface area. Even if you were to attach the radiator directly to the engine, the heat will take time to flow from the inside of the block to the radiator, and there’s not a good, easy way to get air to flow through those parts of the engine.
Coolant is the solution. You pump a liquid through the engine block, where the coolant gets very hot. Then, the coolant goes through a radiator where it gets divided up amongst hundreds of tiny, thin fins that make a ton of contact with the air. The coolant cools down and circles back to the engine.
Just about any liquid can do this, but you do want it to have at least one property which is *being liquid at the temperatures and pressures inside of the system*. Another great property is to be cheap and abundant. Given that car and truck engines have to take a ton of abuse, it doesn’t make a lot of sense to fill up the engine with some super-efficient coolant that you’re going to lose to leaks. Water has both of these properties. And, indeed, car and truck radiators are full of mostly water.
Water does have one unfortunate property that is undesirable, which is that it freezes at temperatures that are very common around the world, at least during some part of the year. So, we add chemicals to the water, which we call *antifreeze*, that prevents the water from freezing. The chemicals have some added benefits, like also helping the water stay liquid as it heats up, helping to lubricate the water pump, and prevent corrosion normally caused by water.
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