An automotive antifreeze chart has information regarding the amount of antifreeze necessary for various cooling systems at different ambient temperatures. For example, in a 12-quart cooling system, four quarts of antifreeze are required at 0 degrees Fahrenheit to avoid frozen water in the radiator, hoses or other parts of the system. Vehicles require larger percentages of antifreeze as either cooling system sizes increase or ambient temperatures decrease.
Generally, as temperatures decrease, the amount of antifreeze, either ethylene glycol or the less-toxic propylene glycol, relative to water in an automobile's cooling system must increase to prevent freezing. Beyond a certain point, increasing the amount of antifreeze stops exhibiting noticeable benefits for the vehicle. The ideal mixture uses one half each of water and antifreeze, but very low temperatures necessitate using more antifreeze.
An automotive coolant mixture should never exceed 70 percent antifreeze to 30 percent water. Not only will adding more antifreeze do nothing more to prevent freezing inside the system, doing so also decreases the vehicle's cooling efficiency. This happens because water freezes at a higher temperature than antifreeze but has a much higher specific-heat capacity, meaning it can absorb significantly more heat before boiling. Using too much antifreeze can potentially lead to overheating, as the system can no longer deal with very high temperatures.