The coolant that passes through the engine and associated plumbing accessories must have the ability to withstand temperatures well below zero without freezing. It must also be able to handle engine temperatures in excess of 250 degrees without boiling. Seems like a long margin for any fluid, but that isn’t all. The fluid must also posses rust inhibiters and a lubricant.
The coolant in modern vehicles is a mixture of ethylene glycol (antifreeze) and water. The recommended ratio is fifty-fifty.
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