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Cooling System

CONSIDER THE RADIATOR A NEW MAINTENANCE ITEM

edited from an article by Gary Goms, Import-Car Magazine June2003

Although radiators aren't glamorous, high-tech replacement parts like wide-band oxygen sensors and Karman-Vortex air flow sensors, diagnosing and replacing them when they become defective is becoming a more important part of import vehicle maintenance today. There are at least three reasons why radiators are becoming important maintenance items. First, late-model imports are now being driven well beyond the normal service life of most radiators. Second, radiators are becoming a maintenance-related item because they often must be removed to replace routine maintenance and failure items like timing belts and water pumps. Third, new radiators are becoming much more affordable than in year's past because of better aftermarket availability and pricing structures.

AS RADIATORS AGE
Because modern aluminum radiators often use a thin-tube design to dissipate heat much more efficiently, they're also more sensitive to internal and external clogging than the old brass radiators of several decades ago. Since the radiator transfers heat between hot antifreeze and cool atmospheric air, it's easy to understand that if either the coolant or air flow gradually becomes restricted, the radiator will begin to lose its heat-exchanging efficiency.

Electrolytic metal transfer caused by a depleted additive package in the old antifreeze mixture usually causes coolant restriction. Bimetallic engines made from aluminum and cast iron are more susceptible to electrolytic corrosion because different metals suspended in a solution tend to create a mild electric current that clogs radiator tubes. When worn-out additive packages allow corrosive ethylene glycol to attack the metals in the radiator, cylinder head and engine block, sediment forms and aggravates the already restricted radiator core tube condition.

External clogging and wear also causes a radiator to lose efficiency. Most external clogging is caused by airborne road debris such as bugs, dirt and airborne plant material. External wear, on the other hand, normally consists of the cooling fins becoming corroded and oxidized to the point that they actually fall from between the radiator tubes. In either of these events, the radiator's heat-exchanging capacity is seriously reduced.

DIAGNOSTIC OVERVIEW
Although radiators don't appear to be high-tech components, they actually become quite complex when various design factors are taken into consideration. Coolant temperature, coolant flow, ambient air temperature, air flow and exposed radiator surface area all come into play when diagnosing a radiator.

A radiator might be in perfect condition but fail to perform if it doesn't meet the auto manufacturer's original specifications. To illustrate, cooling capacity is seriously reduced when a radiator with fewer cooling tubes or heat-radiating fins is installed. The radiator's cooling capacity is also reduced if the fan system isn't performing at rated speed or if, in the case of an SUV, accessories like spare tires are added to the front that may impede air flow.

Last, it's important to mention that a radiator must have the correct antifreeze and water mixture in order to function correctly. Most manufacturers recommend a 50/50 mix of antifreeze and coolant to provide optimum freeze protection and cooling capability. Too much water results in premature boilover. Too much antifreeze reduces the cooling capacity of the radiator. And, since not all brands of antifreeze are compatible with all cooling system materials, it's important that manufacturers' recommendations be followed as to the type of antifreeze being installed in the radiator.

SYMPTOMS OF CLOGGING
A thorough diagnosis begins with evaluating the symptoms of radiator clogging. The most obvious symptom is that the temperature gauge reading is higher than normal on hot days. It also will read higher when operating under prolonged loads or when the air conditioner is turned on. Continued overheating may also cause abnormal coolant consumption.

Perhaps the best method of testing radiator efficiency is to measure coolant inlet and outlet temperatures when the cooling fans are activated. A typical measurement might show 200° F coolant entering the radiator and 130-160° F coolant exiting the radiator. If the difference between the inlet and outlet temperature is too great, it would suggest that a partially opened thermostat or a defective water pump impellor is restricting the coolant flow. If the difference between inlet and outlet temperatures is too small, it would suggest that the radiator itself is suffering from an internal coolant or external air flow restriction.

The best way to measure coolant inlet and outlet temperatures is to use a laser-beam, infrared pyrometer that records minimum and maximum surface temperatures. Since infrared pyrometers are sensitive to the reflectivity of various materials, it's also important to measure temperatures on non-reflective radiator surfaces. In some cases, spraying flat black paint on a small area of the radiator can reduce reflectivity in order to produce a more accurate reading.

TESTING FOR LEAKS
Because modern engine compartments are very crowded, it's often very difficult to detect minor coolant leaks. The most common form of radiator leak test is to use a radiator pressure tester to force coolant through suspected leaks. The hand-pump pressure tester will show a leak as a gradual loss of air pressure (see Photo 1). Pressure testers that attach to a compressed air supply will apply sustained pressures for a long period of time in order to detect small, temperature-related leaks (see Photo 2).

Hand-pump testers also may be used to test radiator caps for both sealing and pressure control qualities. Radiator caps that leak around the top cap seal allow air to enter the radiator during the cool-down cycle. If the coolant level in the recovery tank doesn't increase and decrease in relation to coolant temperature, the cap or coolant recovery system may be defective.

Ultraviolet dye may also be installed in the coolant to help detect intermittent leaks (see Photo 3). For best results, the vehicle should be driven for several days to thoroughly mix the dye with the coolant. Several days of driving may also be required to provide enough heating cycles for the UV dye to penetrate the leak. Ultra-violet detection methods have been simplified recently by the creation of battery-powered, pencil-sized UV lamps that can access every nook and cranny of the engine compartment.

HEAD GASKET LEAKS
Although the topic of cylinder head gasket leak detection is too lengthy to discuss in this space, it's important to understand that head gasket leaks aerate the coolant with combustion gas, which, in turn, reduces the efficiency of the radiator. Head gasket leaks often manifest themselves when excessive coolant is forced into the coolant recovery tank during engine warm-up or when the engine oil acquires a viscous, milky appearance. In most cases, a cracked cylinder head or leaking head gasket also will cause coolant loss, which eventually reduces the radiator's overall cooling efficiency.

TESTING COOLING FAN OPERATION
It's important to remember that modern cooling fans are directly controlled by the engine computer, and that cooling fans may operate under several different modes, including low and high speeds, post-engine shut-off, air conditioning, and during a failure of the engine computer or PCM.

Most modern cooling fan diagnosis may be done with a computer scan tool that allows the technician to either observe the fan's operating status or allows him to use a bi-directional control to activate the cooling fans. In any case, verifying correct cooling fan operation is an important part of radiator diagnosis since the cooling fan is responsible for providing adequate air flow through the radiator during prolonged idling or low-speed operation of the vehicle.

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