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Cooling System
COOLING SYSTEM SERVICE:
PREVENTIVE MAINTENANCE THWARTS FUTURE SYSTEM FAILURES
edited from an article by Gary Goms, Import-Car Magazine July 2002
Cooling System Reminders
By Doug Vidler
The summer months spell warm temperatures and summer vacations. It’s also the time of year for cooling system failures. When gearing up for the "cooling system season," it’s important to remember the components that are required to properly maintain and service today’s systems. With the complexity of today’s systems, it’s easy to uncover additional items that will help keep the engine running cool.
Remember that the engine cooling system on nearly every vehicle built in the last 20 years is monitored by the vehicle’s computer system. Coolant temperature sensors are responsible for converting a temperature value to an electrical value that the computer uses to control a host of outputs. These include fuel mixture, idle speed, EGR, cooling fans, air conditioning compressor and automatic transmission shifting, not to mention open and closed loop status. It has been said that a lack of cooling system maintenance can eventually cause a compromise in the value of the temperature sensor readings.
Other items to mention are more obvious. Wear items such as accessory drive belts and water pumps are easy to spot when they fail, as are radiators. Cooling fans, both electric and thermostatic, are also critical in cooling system performance. The best practice is to catch problems before they occur.
Look for subtle cracks in the belts because they can lead to a complete fracture and failure. Many engines use a single serpentine belt. When it breaks, all driven accessories stop: no water pump, no alternator, no power steering and no air conditioning. Check with the manufacturer’s recommended replacement mileage interval. And remember, the mileage outlined for various services are usually for optimal driving conditions and may not take into consideration severe driving in the desert, stop-and-go city driving or pulling a trailer.
If you’re dealing with an overheating problem, make sure you recommend other parts or services that will not only help address the immediate problem, but also thwart future or repeat failures. Take into consideration the "cascade effect," which occurs when one failure causes a subsequent failure of another system or component. For example, a stuck thermostat may cause the engine to run excessively hot, to the point of overheating. The temperature and pressure may get high enough to cause a radiator hose to fail. When the hose fails, a sudden and rapid loss of antifreeze occurs. When the antifreeze escapes, it saturates the accessory drive belt and may make it unusable.
Recommending the correct and highest quality service components is only part of the responsibility. Discovering the results of a cascade failure is the other part. Cooling system technology is evolving. We’ve seen the introduction of long-life antifreeze/coolant with service life of up to 100,000 miles or more. The system components are continually improving with better heat exchange capabilities and less weight. In the future, you’ll see the belt-driven water pumps evolve into an electric version as 42-volt systems emerge.
Regardless of the technological advances, don’t forget the basics! Be aware of the service and revenue potential from both a maintenance and repair standpoint.
By now, it’s very obvious to most import service shops that cooling system service is an absolute "must-do" on any import nameplate. Once a cooling system suffers long-term neglect, it turns into an on-going source of problems for the owner and his service technician because, when corrosion starts to take place, the effects can’t be reversed. For that single reason, it’s especially important to convince your customers of the necessity of the "Complete Cooling System Service."
CORROSIVE INFLUENCES
Ethylene glycol-based coolants incorporate a considerable additive package that’s designed to control the extremely corrosive tendencies of the coolant itself. The additive package not only prevents corrosion, it also prevents electrolysis, which is the tendency of different metals to dissolve and migrate throughout the coolant. This migration is caused by a mild electric current flow that is caused by dissimilar metals being suspended in a water-based liquid. Thus, when the additive package is depleted, critical gasket sealing surfaces become eroded and coolant passage tubes in the radiator become clogged. In addition, sediment caused by rust from iron cylinder blocks settles to the bottom of the engine’s water jackets, which further decreases the ability of the coolant to dissipate heat.
Once corrosion and electrolysis wreak havoc throughout the cooling system, the future life of the cooling system has been compromised to the point that replacing radiators, heater cores, cylinder head gaskets, and other expensive components will become common practice for the owner. As for water pumps, consider that when highly abrasive iron oxides become suspended in the coolant, the life of any new water pump seal becomes severely limited.
RADIATOR DESIGN
When performing a cooling system service, few technicians really consider how modern radiator design has affected service practices. Years ago, radiators were heavy, vertical core units made of brass and held together with highly toxic lead-tin solder. Eventually, the horizontal-tube or cross-flow design began to dominate the market because it was compact, lightweight, and relatively easy to manufacture using alternative materials like aluminum and plastic.
In order to make radiators lighter and more efficient, manufacturers began making the cooling tubes thinner and packing more cooling fins between the tubes. The downsides of such a design, obviously, are cooling tubes that will clog easily and fins that rapidly accumulate road debris. Because of these two factors, water pumps must develop more pressure to circulate coolant and electric cooling fans must run faster to draw air through denser radiator cores. The objective of any complete cooling system service, of course, is to keep the radiator core as internally and externally clean as possible.
When explaining the complete cooling system service, keep in mind that clogged radiators tend to cause gradual engine overheating, particularly when the vehicle is climbing long gradients over plateaus and high mountain passes. The overheating occurs because a critical number of radiator cooling tubes are clogged. The clogging usually occurs because dirty coolant has been poured back into the radiator after a cooling system component, like a water pump, has been replaced. The clogging may also typically take place after a severe overheating condition has occurred, when sediment from the engine water jackets has been deposited in the radiator core tubes. Although reverse flushing might remove some of the clogging, I would recommend that the radiator either be replaced or repaired, especially if the overheating condition has reached the severe stage.
COOLING FANS
Like the radiator, electric cooling fan performance is often taken for granted. In reality, modern cooling fan design and operating strategy have become very sophisticated. Some fans are designed as two-speed units, with the low-speed application being used, let’s say, 90 percent of the time. The only time the high-speed application will activate is during high temperatures or high loads.
Consequently, when performing the complete cooling system service, it’s very important to test the cooling fan or fan’s operation for its correct programmed operation. In most applications, the cooling fan will activate when the air conditioning system or compressor clutch is activated. Other applications may require coolant outlet temperatures to rise as high as 230° F before the PCM will command the fan relay to close and activate the cooling fan itself.
When testing a two-speed fan application, it’s important to first understand what the operating strategy of the fan happens to be. The high-speed portion of the fan’s controls often can be activated with the bi-directional controls on a scan tool. In other cases, the coolant temperature or throttle opening must be high enough to activate the high-speed portion of the fan.
It’s also important to be aware that high capacity fans draw more electrical current than low-capacity fans. If a low-amperage motor has been substituted for a high amperage application, it won’t properly cool the radiator. So it’s very important never to assume that the fan is operating correctly just because it activates when the engine reaches a predetermined operating temperature.
THERMOSTATS
Several import manufacturers have recently issued statements about severe engine damage caused by the effects of sludging and gelling of crankcase oil in their engines. In my experience, when the water condensation is combined with oil and combustion by-products like carbon and sulfur, the oil thickens into sludge. This sludge accumulates inside the engine and eventually clogs the oil pickup screen and vital lubrication passages.
Gelling, on the other hand, is usually caused by the long-term oxidation of hot oil. As neglected crankcase oil begins to oxidize, it forms a gelatin-like substance that, like sludge, clogs vital lubrication passages in the engine.
It’s important to understand that, while sludging or gelling is primarily caused by neglected or unperformed oil changes, it is also aggravated by poorly performing cooling systems. In years past, engines were operated at 195° F in order to better vaporize the fuel and evaporate condensation from the crankcase oil. In direct contrast, some engine designers are now actually running their engines cooler, often at 170-180° F operating temperature in order to accommodate higher static compression ratios.
Consequently, the role that the ever-so-humble thermostat plays in engine performance and longevity is increasingly important. For example, it's important to verify thermostat operation with a non-contact pyrometer and then compare that temperature reading with the OBD II data stream temperature reading. If either temperature reading doesn’t agree or is out of specification, the engine’s exhaust emissions, performance, fuel economy and overall operating life will be affected. Considering the relatively low price of a quality, OEM-spec thermostat, it wouldn’t be cost prohibitive to replace the thermostat whenever the cooling system is drained for any other service.
BELTS AND HOSES
Clearly, hoses and drive belts are the most under-sold service on today’s import vehicle primarily because it’s not uncommon for many import belts and hoses to look like "brand-new," even after 60,000-80,000 miles of service. Ideally, new hoses should be sold during a water pump or timing belt replacement. In reality, many service writers and techs take a pass on new hoses to keep the estimate low and avoid the perception of selling "unneeded services."
Unfortunately, an aging hose or belt usually breaks at the most inconvenient time and location. To make matters more complicated, most heater, throttle body, and radiator hoses on modern imports are custom-molded, which means that many of these hoses are available only on over-night parts orders.
As for accessory drive belts and timing belts, keep in mind that, depending upon the application, both can drive the all-essential water pump. A failure of the belt means that the vehicle is sidelined until the belt is replaced. Again, serpentine belts are usually application-specific, which means that if the vehicle fails in a rural locality, the driver suffers a major inconvenience.
PREVENTIVE STRATEGIES
The objective of selling the complete cooling system service is to prevent future failures. Indeed, 99 percent of most cooling system failures can be prevented by the simple inspection of the radiator cap, belts, hoses, water pump idler pulleys and coolant condition. If the vehicle hasn’t received scheduled maintenance on its cooling system, it’s time to inspect the system for damage and prepare a service estimate.
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