Coolant
• The effectiveness of a cooling system is also affected by the nature of the coolant itself. In early automobiles, the coolant was usually water. If a vehicle was to be driven in cold weather, antifreeze was added to prevent the coolant from freezing in the header tanks. Eventually, different chemical solutions were experimented with to provide more effective cooling.
Modern coolant is usually comprised of propylene glycol or ethylene glycol. In most cases, a chemical is added to prevent corrosion. This has been standard practice since the introduction of aluminum in the construction of radiators.
Water is still an effective coolant, but will quickly boil off once the engine is run at a regular temperature. However, in emergency situations water can be used to keep a car's engine cool enough to operate and avoid damage.