Why radiators want water as a coolant?

Answer 1

Cars use a 50/50 mix for the most part to cool the engine. 70/30, 70% anti-freeze mixes are used in places that see extremely cold temperatures <-30 degrees F. Normal temperature >-30F, cars don't use 70/30 ratio because anti-freeze is less efficient at cooling than water,. This is why most race cars use very little anti-freeze( mainly for it's lubrication properties) in their cars.

Answer 2

Automotive radiators/cooling systems don't like straight water as a coolant. A mixture of at least 50% clean water and 50% antifreeze is designed to raise the boiling temp, protect the system from freezing, transfer heat energy, lubricate the water pump and adds chemicals to reduce corrosion.

Answer 3

Most don't use water - they normally use an ethylene glycol solution. Water (with an added lubricant for the water pump) is typically used on racing circuits, due to both the better heat transfer properties and environmental concern.
In either case, the purpose is to flow through the engine and absorb heat. It then travels through the radiator, where the heat is transferred to the much cooler ambient air which flows through the radiator fins.