Internal combustion engines produce power by burning the fuel to create a tremendous amount of heat and pressure, which is converted into mechanical energy to move the vehicle. And even with all the wonderful efficiency of modern engines, these are only about 80% efficient in converting fuel energy into useful power. In other words, the motors produce more heat than they can convert into power, so some kind of cooling system is needed to control the operating temperatures and send overheating.
Over the decades, two types of cooling systems have been used: air and water. At the end of the day, all the excess heat produced by an engine must dissipate into the atmosphere. The engines of some vehicles, such as the flat four-cylinder power plant of the iconic Volkswagen sedan, were cooled directly by air flow over the heads and the cylinder block.
There was no separate cooling system to be serviced, there was no refrigerant that had to be purged and cleaned, there was no thermostat that had to be changed, and there was no leaking water pump and it failed; simply a band-driven fan to blow air over the motor. But even with all simplicity, light weight and reliability of air-cooled car engines, they tend to suffer higher operating temperatures with higher losses in performance and fuel economy. And since there is no refrigerant, they are not as efficient in providing heat to keep the cabin and its passengers warm.
Now, cooling by air is still popular in the smaller engines found in lawn mowing and gardening equipment. Most motor vehicles have closed cooling systems that make use of some liquid. The water pump circulates the coolant through the block and the cylinder heads to absorb and carry excess heat from the combustion to the radiator, which sends the heat to the atmospheric air that moves through its fins and cores cooling.
To help the efficiency of the cooling system that uses a liquid, the system is pressurized and controlled with a thermostat. By operating the system at higher pressures, typically in the range of 7-16lb / in², the boiling point is raised to 205 degrees Fahrenheit (120 degrees Celsius) or at a higher level, the refrigerant will not boil or lose efficiency at temperatures Normal motor operation of 180-230 degrees Fahrenheit (82-110 degrees Celsius). The pressure is controlled by the pressure cap on the radiator or the recovery tank.
Because internal combustion engines do not operate efficiently or cleanly in terms of emissions until they reach full operating temperature, a system thermostat restricts the flow of refrigerant until its temperatures reach the normal range. From this point on, the thermostat begins to fall below the normal value threshold, usually around 120 degrees Fahrenheit (82 degrees Celsius).
A final component of the cooling system is the refrigerant itself. Believe it or not, as far as pure cooling efficiency is concerned, water is the best option. Its ability to absorb heat quickly and efficiently, together with its abundance and low cost, makes it the perfect coolant, with two exceptions. Water freezes at temperatures of 32 degrees Fahrenheit (0 degrees Celsius) or lower, and tends to promote corrosion.
That is why to avoid corrosion in the cooling system, the refrigerant is incorporated a package of additives that include oxidation inhibitors and a lubricant for the water pump. Historically, oxidation inhibitors have been phosphates, borates and silicates. Today these are still popular, but many automakers are filling their cooling systems with long-life coolants that use different chemical components to prevent corrosion.
Probably the best known is Dex-Cool used by General Motors. It remains an ethylene glycol antifreeze, but uses an organic carbon compound to reduce the components and protect them against corrosion.
Leave a Reply