The term antifreeze is often used interchangeably with the term coolant. As confusing as that might seem, both terms are correct. Antifreeze refers to the liquid that is used as a heat transfer medium between the engine and radiator in order to cool the car's engine and prevent overheating.
As its name suggest, antifreeze provides a reduction in the freezing point of the liquid. Modern antifreeze also offers an increased boiling point, which, combined with a pressurized cooling system, allows the car's engine to run hotter. The increased working range of the engine coolant allows for improved reliability in cold weather and for improved vehicle fuel economy.
Antifreeze was first based on ethylene glycol, but in more modern and ecologically minded fluids this may be based on propylene glycol. These compounds are usually only run in a 50/50 mix with water. Water actually provides excellent thermal transfer capabilities so there is little advantage to using any concentration of antifreeze beyond what is required to inhibit freezing.
Vehicle manufacturers will include different additives to increase compatibility and reduce corrosion of the various materials used in the car's cooling system. This is why it is important to only use the manufacturers recommended coolant. Antifreeze is often colored in such a way as to make it easier to identify the correct replacement fluid. You may have noticed this before: some antifreeze mixtures are pink, while others are green. This is important to know also, as some incompatible antifreeze blends can case a chemical reaction and turn into a gel which blocks the cooling system.
It is important to keep tabs on the coolant level in your vehicle as the consequences of an overheated engine can be very costly. For safety sake, be sure to only check your coolant level when the engine is cold. Opening the cap on a hot engine can cause a sudden release of pressurized coolant from the radiator and coolant reservoir. This can cause serious injury. If your find your car to be low on coolant, consult your owner’s manual to ensure that you top up with the correct antifreeze.