Taking a sample reading using...
Taking a sample reading using a refract-ometer came next. The coolant from the engine is placed on the glass and the moisture content is measured in a scale identified as Brix.
The scale that surface tension is measured in is dynes/centimeter. Water has a very high surface tension (72 dyn/cm), which makes it a poor choice for an engine coolant. A mix of EG and water (50/50) has a reading of 56 dyn/cm, while the Evans NPG+ is much easier to release at 44 dyn/cm.
The Boiling Cycle
The coolant used in an engine undergoes a boiling phase that is required to remove heat from the cylinder head. Up until very recently, the premise of most cooling system designs was to eliminate or not allow boiling to occur. In simple terms, the idea of having boiling coolant in an engine was thought of as the result of either poor engineering or a component failure. Those readers who are older will remember the dreaded "boilover" that would occur and leave motorists stranded on the side of the road, waiting for the engine to cool and figuring out how they would transport water from a nearby stream or lake into their vehicle's radiator.
When it comes to boiling, it's true that it's not desirable to have this occur in the radiator. The radiator's job is to cool the liquid, while the liquid's task is to cool the engine. If the radiator of an engine is boiling over, it means the coolant is becoming superheated and turning to a vapor, and when it recondenses, it contains too much heat for the radiator to dissipate. So as you can see, we need to identify when it is good and sound engineering to have the coolant boil.
Before this topic can be explored, it needs to be recognized that the load on the cooling system and the coolant itself are not the same under all driving conditions. At idle and light load, such as cruising down an interstate highway, the engine is not required to produce much power. At 65 mph, the power required to move the vehicle is only a fraction of what the engine can produce at maximum output. On the average, an older Pontiac only requires 25-30 hp to cruise on level ground at 65 mph. Since an internal-combustion engine is nothing more than a heat pump, the thermal load the liquid coolant and the radiator, is exposed to is proportional to the heat of the power produced. If the same vehicle is asked to climb a long grade at a steep angle, pull a trailer, or produce maximum power for passing or racing, then the load on the coolant and radiator increases.
A coolant must work to meet the transient needs of the engine. Many falsely believe that water is the best coolant since it has a specific heat of 1. That would be true if the engine that it was used in was going to do nothing but idle or never produce anywhere near maximum power during its lifetime. With a specific heat of 1 and good thermal conductivity qualities, water does an excellent job of cooling an engine; that is, until the load is increased and the coolant starts to boil in the cylinder heads. Never mind the fact that water creates rust and corrosion that insulates the liquid from the water passages, diminishing thermal transfer in the engine and radiator. When this happens in the engine, the water would stay cooler since there is less heat rejected into it, but the metal surface temperature of the cylinder head would be much higher. In addition, water offers no lubrication properties for the pumping mechanism (water pump) and will freeze when cooled.
Traditional antifreeze that is a mix of EG and water solves some of the problems of pure water, but brings along its own set of issues. Water by itself has a very high surface tension, and when it does boil, it's harder for it to release and recondense back to a liquid. Thus it has limited ability to remove heat from the boiling point area and follow the laws of physics.