Pure antifreeze, which is the chemical ethylene glycol, has a boiling point of about 388.4 degrees Fahrenheit. However, most coolants are made of a combination of ethylene glycol and water.
A common mixture in a car radiator is 50 percent ethylene glycol and 50 percent water. This mixture has a boiling point of 223 degrees Fahrenheit. A mixture of 70 percent ethylene glycol and 30 percent water has a boiling point of 235 degrees Fahrenheit. Coolant should be about 200 degrees Fahrenheit for engines to run optimally.
A less-common type of antifreeze contains propylene glycol instead of ethylene glycol. This type has a boiling point of 370.8 degrees Fahrenheit.