The precise amount of antifreeze a radiator holds depends upon the size and make of the car, but the solution in a car radiator should be a mix of about 50 to 60 percent antifreeze and 40 to 50 percent water. Freeze protection doesn't improve by running the engine with a higher percentage of antifreeze.

The ingredient that extends the freezing point of the coolant is ethylene glycol, which by itself doesn't wear out or need to be replaced. However, other chemicals in the coolant are corrosion and rust inhibitors, which wear out and require periodic changes of antifreeze. The differing colors of antifreeze result from the inhibitors they contain. They aren't interchangeable, as some are made for aluminum radiators and others for copper and brass radiators. The correct antifreeze and the timing of replacement is based upon the type of car and the materials with which the radiator is made.

Various types of antifreeze shouldn't be mixed with each other. To switch over to a different type of compatible antifreeze, it is necessary to flush the cooling system thoroughly with pure water, warm up the engine, let the water cool, then drain. Afterwards, the new antifreeze and water in the correct mix can be added to the radiator.