I called Mike Tourville, marketing manager for Evans, and asked him if he could explain further. I had to confess that I had never worked on water-cooled engines. My only experience with engine overheating, engine knocking, and loss of coolant was when I was driving in the White Mountains in California. I had to stop the car because the radiator boiled over and was hissing like an old steam locomotive. So, thanks to Tourville’s explanations, along with additional documents from the company’s chief engineer, Thomas Light, I was able to understand the science behind my hissing radiator. My suspicions about this involving physics was also confirmed by the document that Light sent containing short sentences and small simple words.
Limitations of water-based coolants
According to Tourville, “Nucleate Boiling” is what occurs when liquid coolant comes in direct contact with the hot metal of the engine that has reached or exceeded the boiling point of the coolant. Heat is absorbed into this layer of liquid coolant from the metal surfaces of the engine. This is a good thing because a lot of heat moves from the metal to the coolant as the coolant converts from liquid to vapor. It is not a good thing, however, if the conditions don’t exist for the vapor to readily condense back to liquid. As engine temperatures rise, the limitations of traditional water-based coolants can be quickly reached. This condition is made worse when an engine is stressed by hauling heavy loads, traveling steep grades, or in high altitudes.
The limitation is the relatively low boiling point of water. When there is very little separation between the operating temperature of the coolant and the boiling point of water, the cooling efficiency of the system declines and engine temps begin to climb. When water is boiled, it produces vapor which causes a sharp decline in effective cooling, and often the failure of the cooling system. Water vapor has almost no thermal conductivity. If the water vapor cannot condense, then you get in a loop where the water vapor makes an insulating barrier between hot metal and liquid coolant. The hot metal does not get a flow of coolant, making the temperature of the metal spike higher.
Some locations within the engine (hot spots) generate temperatures that can result in local coolant boils, creating nearly 100 percent water vapor. These hot spot results in pre-ignition (“knock”), and if this condition continues, then structural metal failure and engine shutdown can occur. I get the engine knocking part, but what about my car that turned into a hissing dragon up in the White Mountains? Again, the root cause is the boiling point of water. The boiling point of water declines as altitude increases. Just as water vapor in the cooling system can cause hot spots and engine knocking, it can also cause coolant pump cavitations when the engine is running, and create after-boil when the engine is shut down. According to the Evans experts “the action of the coolant pump creates a low pressure area at the pump inlet. Pump cavitations occurs when coolant near its boiling point encounters the low-pressure area, and flash vaporizes within the pump. The gas pocket in the pump causes the pump to stop functioning and coolant circulation to stop. Coolant pump cavitation leads directly to catastrophic cooling system failure, with the coolant being expelled from the system as steam as pressure exceeds the pressure relief setting of the cap.”
The experts also explained that after-boil occurs after shutdown of a stressed engine, when the coolant is near its boiling point, and residual heat remains in the cylinder head or in an auxiliary circuit such as an EGR cooler. “Upon shutdown the coolant pump ceases to circulate coolant through the cooling system. Residual heat boils the stagnant coolant, making steam pressure that exceeds the pressure relief setting of the cap.” Coolant is pushed out of the system, hence my hissing dragon car. Remember when I said earlier that you can operate Evans waterless coolant systems at low pressure? After learning about the limitations imposed by water-based coolants, I also wanted to know why a waterless coolant is so much more effective, and why not use it in all internal combustion engines?
Advantages of waterless coolants
Thomas Light, Evans’ chief engineer, explains, “Cooling systems using water-based coolants are operated near the boiling point of water for the pressure of the system. In contrast, an Evans waterless coolant is operated at a temperature that is much colder than its high boiling point. Consequently, condensing vapor from an Evans coolant is very easy to accomplish. Hot spots are prevented by keeping liquid coolant in contact with all of the hot metal areas all of the time.”
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