Water turns into steam at 100°C. Mixing traditional ethylene glycol coolant with water in a 50-50 ratio increases the boiling point to 106°C, which is close to the operating temperature of an engine.
Evans waterless coolants have a boiling point of over 190°C, far above the operating temperature of the engine. The high boiling point ensures that the coolant remains liquid at all times, enabling consistently effective cooling.
The Science of Overheating
Since the 1930s, engine coolants have been based on a mixture of ethylene glycol, water and corrosion inhibitors. All such mixtures have inherent physical and chemical limitations that restrict engine performance and affect reliability.
Traditional water-based antifreeze regularly crosses from efficient nucleate boiling, where the vapor finds liquid coolant cold enough to condense it, to a vapor insulating condition, where the liquid coolant is not cool enough to condense the vapor and a pocket of vapor forms that insulates the hot metal from the liquid coolant. Compared to liquid coolant, water vapor conducts heat very poorly, about 97% worse. The hot metal gets hotter, making a "hot spot" that causes detonation issues. Evans coolants avoid vapor insulating conditions because any vapor condenses immediately into liquid coolant.
This overheating and excessive thermal stress leads to several problems, including:
- Distortion of the cylinder head and liners
- Pre-ignition (engine knock) in carbureted engines
- Reduced combustion efficiency and detonation issues in fuel-injected engines
- Erosion caused by pitting around the liner, cylinder head and coolant pump
- Cavitation caused by vapor escaping due to pressure drops within the cooling pump
- Boil-over during operation and after-boil when the engine is stopped
Industry sources state that overheating is the most common cause of engine down-time and responsible for more than 40% of catastrophic engine failures.
About Pressurized Caps
Using a pressurized radiator cap can raise the system pressure and thus the coolant boiling point. A typical 1 Bar (14.5psi) pressure cap theoretically raises the boiling point of 50-50 coolant to 123°C, which you would expect to be sufficient to prevent boiling. In reality, pressure drops within the cooling system combined with very high metal temperatures adjacent to the combustion zone often result in boiling coolant and the formation of steam-vapor pockets. Once a steam-vapor pocket is formed, it will not readily condense and can lead to full-overheat, piston-liner scuffing, cylinder-head warping and eventually total engine failure.