Winter poses a variety of challenges for car owners, one of the most important being maintaining the normal operation of their cars' engine cooling systems. Coolant, or antifreeze, plays a key role in this process, especially in low temperatures. Coolant freezing can have serious consequences for a car—when coolant freezes, it expands. This expansion can cause cracks or even rupture the radiator, pipes, and other parts of the cooling system. Repairing such damage can be expensive and difficult.
Factor 1 - Freezing point.
Antifreeze concentrate consists of 92% ethylene glycol, 5% additives (corrosion inhibitors + anti-foaming additive + anti-cavitation additive + dye + vomiting additive) and 3% water. Without the addition of water, this solution freezes at -15 °C. This freezing point is not acceptable for use in the harsh winter conditions of Ukraine, as the crystallization of undiluted concentrate can lead to mechanical damage to the engine cooling system components. The figure below shows the freezing point of undiluted antifreeze concentrate as a red dot.
Factor 2 – Specific heat capacity.
Studies have also shown that the specific heat capacity (the amount of heat absorbed by antifreeze when heated by 1 °C) of the concentrate is 22% worse (i.e., lower) than that of the recommended 50% mixture with water (1:1 dilution to obtain a freezing point of -38 °C) at a working temperature of a warmed-up engine of 95 °C. This means that undiluted concentrate will remove heat from the engine less efficiently than diluted concentrate. The engine will overheat, the engine oil will “age” faster, the cooling system fan will run more often to lower the antifreeze temperature, fuel consumption will increase, and the antifreeze itself will operate at higher temperatures, which will lead to the activation of additives and a faster loss of its operational properties. The figure below shows how much the specific heat capacity of an optimally diluted concentrate differs from that of an undiluted concentrate.
Specific heat capacity J/g·K 
Factor 3 – Viscosity.
The viscosity of antifreeze concentrate (e.g., G12+) at a temperature of -10 °C is approximately 15 times higher than the viscosity of the same concentrate diluted with water 1:1 at the same temperature. Excessive viscosity of the coolant leads to a deterioration in heat transfer due to a slowdown in flow and also leads to premature failure of the pump that pumps the liquid through the system.
Therefore, from an economic and thermodynamic point of view, it is optimal to dilute the concentrate with water in a 1:1 ratio. It is strongly not recommended to pour undiluted antifreeze concentrate into the car's cooling system.