The two primary symptoms of automotive cooling system failure are leaks and an overheated engine. Corrosion is the most common issue, largely caused by a lack of and improperly done maintenance. Properly replacing coolant is far more complex than most people realize.
What is corrosion?
Many forms of corrosion exist, but the technical differences are not pertinent to this discussion. The metals used in automobiles, were not always in their present state. For instance, aluminum started life as bauxite ore. Energy, in the forms of heat and electricity purify the ore and produce aluminum metal. Outside forces cause the energy to leave the aluminum over time and it degrades from the metal state. This is a very simplistic view of corrosion.
Many factors greatly speed up the process. One is heat, always available in the cooling system of an automobile. Air, which enters the system through leaks or improper-service, drastically accelerates corrosion. Another major factor is the presence of different metals in a single system.
Each metal has a propensity for corrosion that they list on a scale, from most noble to least. The more noble metals, like gold and platinum hardly corrode at all. The further apart the metals rank on the scale, the greater they affect one another when placed in electrical contact.
For instance, iron, which is often used in engine blocks, is a more noble metal and aluminum is a more reactive metal. An aluminum radiator or heater core will act as an anode, when placed in electrical contact with iron. The iron components become the cathode and electrons (energy) move from the aluminum and to the iron. This is galvanic corrosion and the effect is to produce holes in the aluminum components.
Why corrosion is much more prevalent today
Engineers select metals to suit their purpose, within limits. For instance, a radiator must conduct heat. Copper is an excellent conductor of heat. In the past, copper radiators and heater cores were common. Aluminum is also a good conductor, is lighter than copper and cost less. To save costs and weight, a more reactive metal is chosen. To prevent corrosion, a very specialized set of chemicals are added to the water used to cool the engine. Without this protection, water would very quickly destroy the metals in a modern cooling system.
When cooling system components corrode they start to leak. Corroded aluminum is not repairable on automobiles and they need expensive replacement. With heater cores, intake manifold and cylinder heads the cost can exceed the value of the vehicle. Leaking core plugs often require engine removal to replace. Neglected cooling systems can easily make a vehicle economically unfeasible to repair.
Coolant today is far more than antifreeze
Water in the cooling system transfers heat from the engine to the radiator, where we remove it. Pure distilled water does a great job of transferring heat, but also has undesirable properties. Water freezes when the temperature drops to 32 degrees Fahrenheit. This causes water to expand and it will crack the engine block. Coolant contains antifreeze chemicals that lower the freeze-point and prevent this problem. The more coolant, in relation to the water, the lower the freeze-point of the mixture.
We can test the effectiveness of the antifreeze portion of our coolant with a hydrometer. These instruments come in various types and measure the specific gravity of liquids, such as coolant. Specific gravity relates to freeze points in coolant and temperatures highly affects the measurement. We should test coolant at room temperature as the reading changes with heat. It is also important to realize hydrometers do not give precise readings. Many testers vary several degrees from actual. Allowing at least ten-degrees safety-factor is best. For instance, if we require -15 degrees of protection, the test should show at least -25 degrees.
Freeze protection is an important function, but only a small part of what coolant does. Coolants of the past contain phosphates and silicates that protect metals. When cooling systems had fewer active metals, these did an okay job. Today organic acids and hybrid organic acids are more often used. These modern coolants etch the surfaces of the metal they protect, forming a coating that prevents electron flow.
Over time we deplete the corrosion protection while protecting the metal. Before this occurs, we should replace coolant. Preventing corrosion is far easier than treating it or replacing damaged components.
When should we replace coolant?
The best guide for replacing coolant is time. Many coolants today are long-life formulations. They will work well for up to five-years, in the original application. When the vehicle is new, long-life coolant protects metal from corrosion for about five years. This is not so on subsequent changes. Protection on a system will last about three years, after we service it. Because the metals are older and have been subjected to the forces of corrosion, protection does not last as long. With a system that is run to the point of depletion, change intervals are much shorter.
Testing pH and electrical conductivity gives an idea of coolant condition. New coolant has a pH around 9.0. As corrosion protection depletes, the pH becomes more acidic. A pH reading below 7.0 means the coolant has depleted the reserve alkalinity. Detecting depleted coolant by sight is impossible. The color may look fine and the pH may be dangerously low.
Getting perfect results with pH and electrical conductivity tests is difficult and accurate equipment is expensive. Time is a better guide for most home mechanics. Mileage is much less of a factor with coolant life. Because it is a chemical reaction, depletion of corrosion protection occurs 24/7. This is true whether we operate the vehicle are not. For example, we may seriously deplete coolant in a six-year-old vehicle, with 30,000 miles.
What type coolant is best
Engineers formulate coolants, using many factors not available to the average person. Many different specifications exist and this information is often difficult to find. The best coolant to use is the one produced by the manufacturer of the vehicle. Using the manufacturer’s product insures the coolant will meet the proper specifications. Aftermarket and universal coolants may not meet the necessary standards.
Many vehicle-specific coolants exist. Using the exact formulation is very important. This changes with year models and even between models in a given year. For instance Ford uses three coolants, in different models and in a single year.
Preventing cooling system corrosion is easy when we replace coolant before depletion. Properly replacing engine coolant is the topic of part II.