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Coolant or Distilled Water – Which is better?
This is a great article that easily explains the benefits of running a water-only setup for performance applications. You can use this information applicability into our cooling systems to further enhance your air to water cooling setup.
Writer: Marlan Davis – for Hot Rod Mag.
The specific heat capacity of ethylene glycol based water solutions is less than that of pure water; in a 50 percent solution, ethylene glycol’s specific heat capacity compared with pure water is decreased at least 20 percent at 36 degrees and about 17 percent at 200 degrees. Propylene glycol, another common coolant, has an even lower specific heat. Assuming a 100-gpm (gallons/minute) coolant flow rate and an energy loss through the coolant system of 189.5 hp, the water temperature increase would be 10 degrees, the ethylene glycol water mix would gain 20 degrees, and propylene glycol would gain 33.3 degrees.
Compensating for the reduced heat capacity of coolant/water mixes would require circulating more fluid through the system. Assuming a fixed amount of circulating fluid and radiator capacity, running 100 percent water would be the most efficient coolant in terms of its ability to conduct heat with minimal temperature rise. In other words, of all common liquids, water requires the most heat energy to change its temperature.
However, there are also differences in the vapor point of the three different coolants. Ethylene glycol and propylene glycol have higher vapor points and therefore can absorb heat at higher temperatures without boiling. Yet even with its lower vapor point, water still carries more heat per unit.
Don’t forget that the coolant is just one part of the total cooling-system “team.” You can raise water’s effective vapor point by using a higher-pressure radiator cap. For every pound of increased system pressure, water’s boiling point goes up by 3 degrees. Higher boiling points also reduce evaporation losses, water-pump cavitation, and heat-soakinduced after-boil. You can get away with a higher system pressure by using a quality aluminum radiator that’s rated for higher pressure than is a brass/copper radiator. Aluminum radiators can take more pressure because their tensile strength is greater than brass—this lets an aluminum unit use tubes with larger cross-sections an thinner walls. A larger tube also has more wall-surface area, resulting in improved heat transfer.
Bottom line: A large-tube aluminum radiator filled with pure water and using at least a 20-psi cap is by far the best heat-transfer setup, provided the vehicle is not subject to freezing conditions. Be sure to add a corrosion inhibitor when running pure water.