A mix of 50 percent antifreeze to 50 percent water is usually sufficient in most areas. In more extreme climates, the mix may be different and must be altered to suit that climate.
Modern antifreeze no longer just protects an engine from cold temperatures. It also raises the boiling point of the water to enable better summer cooling. Most cars manufactured after 1998 require an antifreeze which contains silicate-free, organic acid technology. Too little coolant in a car can cause the car to blow out cold air through the heater and the temperature gauge to read cool. This is because there is no hot water going thorough the heating matrix, and the temperature sensor needs to be in water for it to read accurately.