Industry experts estimate that about 40 percent of engine downtime is caused by cooling system problems. Understanding the common problems and implementing proven preventative maintenance practices significantly reduces operating costs.
There are four major cooling system problems that result in unscheduled downtime, says Sean “Marty” Martinelli, OEM account manager at Penray. They are: cavitation-erosion, corrosion, scale and green goo or drop-out.
Headquartered in Elk Grove Village IL, Penray has been the standard of excellence in cooling and fuel system treatments that maximize performance and help extend vehicle life.
“One of the most common and costly results of improper cooling system maintenance is the perforation of wet-sleeve cylinder liners, often referred to as cavitation-erosion or liner pitting,” says Martinelli. “The perforation is caused by repetitive pitting of the liner as a result of liner vibration.”
As the fuel inside ignites, the liner vibrates within the block, he explains. The outside wall of the liner actually moves away from the coolant causing a near vacuum for an instant. This low pressure causes the surrounding coolant to boil, forming tiny bubbles.
“The liner then returns to its position at extremely high velocity, pressing against the bubbles with a violent force,” says Martinelli. “The bubbles implode against the liner wall surface at pressures up to 60,000 psi. The collapse of these bubbles blasts small holes in the cast iron liner.”
This pitting process will repeat, digging tiny tunnels through the liner. Eventually, the liner wall will become perforated, allowing coolant to enter the combustion side of the cylinder, he says.
“If coolant enters the combustion side of the cylinder, an expensive in-frame overhaul is required. Cavitation-erosion is not usually covered under engine warranties and can take a significant bite out profits.”
Corrosion - the natural tendency of metals to revert back to their ore form - is another problem with an unmaintained cooling system, says Martinelli. A number of conditions in a cooling system will affect the degree and rate at which metal surfaces corrode. These include:
- Coolant pH.
- Concentration of dissolved oxygen and carbon dioxide.
- Metal surface deposits.
- Metal stress.
- Coolant temperature.
- Corrosion inhibitors present.
“All the metals in a cooling system will corrode under certain conditions,” he notes. “Some metals are more sensitive than others. When metals corrode they weaken, and the component will eventually fail.”
The metal most prone to corrosion in a cooling system environment is aluminum, says Martinelli. Cast iron, solder, steel, copper and brass will also corrode.
Hard water scale can block a cooling system’s ability to transfer heat, resulting in overheating.
A diesel engine generates enough heat to warm a seven-room house during the winter, he says. The engine must shed some of this heat to operate efficiently and prevent severe component damage.
“Two-thirds of this heat is lost through the exhaust and through the engine work. The remaining third must be pulled from an engine by the cooling system.
“It is critical that all cooling system heat exchange surfaces remain clean,” he goes on. “Only 1/16 inch of scale will reduce cooling system heat transfer efficiency by 40 percent.”
Martinelli says cooling system problems that result from overheating caused by scale are:
- Severe pitting of the wet sleeve liners.
- Cracked heads and warped engine blocks.
- Oil temperature running abnormally high.
- Failure of the cooling system fan to turn on.
- Scale deposits on cooling system block heaters.
- Corrosion of the steel and cast iron surfaces.
- Hard water scale build-up on the cold side of the liner, creating an insulating effect and consequent hot spots.
- Fouling of the heater core with silica gel and phosphate sludge, resulting in reduced heat to the cab and bunk heaters.