The difference between antifreeze and coolant

No, coolant is not the same as antifreeze. Antifreeze is a concentrated, glycol-based fluid which only when it is diluted with water becomes referred to as coolant.

Coolant is a solution containing water and antifreeze. Water is one of the best ways to keep engines and closed systems cool however, water on its own boils at 100°C  (easily reached within an engine) and freezes at 0°C so requires an additive (antifreeze) to help keep it free flowing across a wider scale of temperatures.

Antifreeze is a concentrated glycol-based fluid typically consisting of ethylene glycol or propylene glycol . In application-specific formulas a specialised inhibitor is also added to help protect system metals from corrosion.

Antifreeze is a dual-purpose product. The primary purpose of which is to prevent coolant from freezing in low temperatures and, on the other end of the spectrum, raise the boiling point of coolant to prevent over-heating.

However, it is worth noting that unless pure antifreeze is diluted with water to create coolant it will not be completely effective in either of these actions. Once mixed with water the solution has a far greater boiling point and much lower freezing than neat antifreeze on its own.   

There are a number of reasons why it isn’t a good idea to use 100% antifreeze. Firstly, the freezing point of neat antifreeze is a lot higher than when you mix with water. For example, pure ethylene glycol will freeze at around -12°C but when mixed with water at a 50/50 ratio the freezing point drops to about -36°C .

Additional to this, neat antifreeze lacks heat transfer capabilities, compared to a antifreeze/water mix. Neat antifreeze loses about a third of its heat transfer capabilities compared to a coolant solution. 

Neat antifreeze is also unable to keep corrosion inhibitors (additives such as silicates, nitrates and phosphates) suspended and free flowing around the cooling system resulting in poor protection against rust, deterioration and build-up. This is why it is always recommended to shake or mix a coolant solution before adding to a system.