Which solution would provide the highest level of antifreeze protection?

A 50/50 solution of ethylene glycol (EG) and distilled water offers optimal antifreeze protection, balance, and boiling point elevation for a variety of conditions encountered in engine cooling systems. This mixture combines the beneficial freezing point depression and boiling point elevation characteristics of ethylene glycol with the ability of water to effectively transfer heat.

Using pure distilled water does not provide any freezing protection and could lead to overheating due to its low boiling point. A 100% solution of propylene glycol (PG) provides some level of antifreeze protection but is generally less effective than EG, especially at lower temperatures. A 100% solution of ethylene glycol, while offering stronger antifreeze capabilities, does not facilitate heat transfer as efficiently as a mixture since the presence of water improves thermal conductivity. Thus, the 50/50 solution achieves a balanced performance, providing sufficient protection from freezing and effective cooling, making it the most effective choice.