Radiator Diagnosis, Repair, & Replacement Tips
Ordinary leaks are easy enough to diagnose because they're hard to miss. A leak of any size at all will weep, drip or spray coolant. The resulting loss of coolant usually leads to engine overheating, which can cause more damage if the leak isn't found and fixed. Leak inhibiting additives can usually seal small leaks. But sealers are a temporary fix and more of a do-it-yourself product. Even so, some professionals recommend using a sealer for preventative maintenance and to prevent or seal porosity leaks in aluminum cylinder heads. Some types of sealers, though, may increase the risk of deposits forming in the cooling system, which could cause radiator clogging - especially if the cooling system is over-dosed with such a product.
Leaks caused by internal corrosion may be found almost anywhere on a radiator. The most vulnerable points are usually the seams and where the tubes are joined to the headers. The underlying cause is almost always cooling system neglect, but it may also be due to bad ground connections between the engine, charging system and vehicle body. If the coolant has been changed regularly and tests good, check the engine's ground connections and clean and retighten as needed.
Solder bloom is a type of internal corrosion that can form when neglected coolant, rust and some types of leak inhibitor additives react with the soldered joints in a copper/brass radiator. White to green crumbly deposits begin to grow, which can block tubes and restrict the flow of coolant. A radiator with this kind of problem must be recored or replaced. The cooling system should be cleaned and flushed to remove deposits and sediment.
Leaks caused by punctures in an otherwise health copper/brass radiator can usually be patched by soldering, brazing or even sealed with epoxy or specially-formulated high temperature hot-melt adhesive (which is not the same kind of adhesive used in a home hot glue gun). If the radiator is full of corrosion, though, a patch is not going to last. The radiator will have to be recored or replaced.
Aluminum radiators can also be repaired by soldering, brazing or welding, but it takes skill and special materials. Epoxy or a special high-temperature hot melt wax are other repair alternatives that can achieve good results on aluminum.
Leaks in plastic end tanks can be filled with epoxy, covered with fiberglass and epoxy, or hot-air welded using nylon plastic filler rod. Welding plastic takes some skill and requires careful surface preparation to get good adhesion. The leak must first be "V" ground and sanded, then cleaned with wax and grease remover to assure a strong bond. The other alternative is to simply replace the damaged end tank. But the job is harder than it looks because the end tank must be pressed down on the core with about 150 lbs. of pressure while the header tabs are clamped in place. Radiator shops have the proper fixtures for doing this, but many underhood repair shops probably don't.
Leaks can also be the result of fatigue cracks from vibration, mechanical stress or collision damage. This type of failure is most often found where inlet and outlet fittings connect to end tanks, along tank/tube header connections, or where the radiator support brackets attach to the radiator. This type of damage can be repaired as long as the radiator is otherwise in relatively good condition. Splits in radiator seams or between the tubes and header may be the result of too much pressure in the cooling system. This may be caused by using a pressure cap with the wrong rating (a 15 lb. cap on a system that's rated at 5 lbs.), or by combustion chamber leaks that allow exhaust to enter the cooling system. Pressure testing the cooling system will tell you if there are any internal coolant leaks, and pressure testing the cap will tell you if it has the correct rating.
Excessive heat can be another cause of radiator failure. Radiators with plastic end tanks are very vulnerable to steam erosion. If the coolant level is low and the engine starts to run hot, steam can erode and melt a hole right through an end tank. White deposits on the inside of the plastic is evidence that hot steam rather than coolant was flowing into the tank. If you find this kind of damage, check the thermostat and pressure test the system for leaks after the radiator has been repaired or replaced.
A clogged radiator may look fine on the outside but allow little coolant flow
and heat transfer because of plugged tubes. Coolant neglect is the underlying
cause. The radiator should be removed and sent to a radiator shop for cleaning,
or replaced. The cooling system should also be cleaned and flushed to remove
deposits and sediment.
When replacing a radiator, the width, height and thickness of the old and new units should be fairly close but may not always be an exact match because of consolidation (especially if you're replacing an aluminum radiator with one made of copper/brass or vice versa). Even so, the cooling capacity of the replacement should be the same or greater than the original.
When bolting the radiator in place, check for misalignment between the mounting brackets and radiator support. Misalignment can crease stress that may lead to fatigue cracking and radiator failure.
Inspect the condition of all belts and hoses. After four years of service the incidence of failure goes up dramatically. So if these parts have not been replaced, recommend new belts and hoses for preventative maintenance. Also, make sure hoses are properly positioned and supported to minimize stress on the radiator connections.
Make sure you replace the fan shroud or any other ducting that was originally on the vehicle. Leaving off a fan shroud can significantly reduce the radiator's ability to cool the engine at low speeds when most of the airflow is generated by the fan.
A new cap is recommended with a new radiator. But if you're reusing the old cap, pressure test it to make sure it is still holds the proper pressure.
If the engine has overheated, the thermostat should probably be replaced to eliminate any possibility of a comeback. Installing one of the new "fail-safe" designs can reduce the risk of engine damaging overheating should the unit ever fail.
When refilling the cooling system, use a 50/50 mixture of fresh antifreeze and clean water (distilled water is best). Getting all the air out of the system is a must, so make use of any air bleeds that are provided. If there are no air bleeds, you may have to loosen and "burp" a heater hose to get all the air out. Some thermostats have a jiggle pin or small bleeder hole that vents air making filling easier. Others do not, and can trap air causing the engine to overheat.
Check the operation of the cooling fan - especially if the engine overheated. On older rear-wheel drive vehicles with a fan clutch, check for clutch slippage or fluid leakage. Fan clutches lose their grip as they age, and can be a common cause of overheating.
Also, don't overlook the coolant reservoir. The reservoir serves as a storage tank for excess coolant and works with the pressure cap to keep the system full of coolant. If the reservoir is damaged or full of sediment, replace it. Small leaks in the reservoir can be repaired with silicone glue. Also, make sure the hose between the radiator cap and reservoir is in good condition, properly routed, free from kinks or obstructions.
Aluminum vs. Copper/Brass
Aluminum prevails as the most common material used for passenger car and light truck radiators today. Though you may think aluminum radiators are relatively new, the first ones were used way back in 1913 by Rolls Royce. Copper/brass has been the material of choice for most radiators until recently because of its superior ability to conduct heat (twice as good as aluminum), greater strength/corrosion resistance and lower cost.
In the 1960s General Motors introduced aluminum radiators on the Corvette as a means of reducing weight. A typical radiator that weighs 15 lbs. in copper/brass weighs only about five and a half pounds when made of aluminum. European auto makers began using some aluminum radiators in the 1970s, but use here was very limited until the 1980s when the push to improve fuel economy began to tip the scales in favor of aluminum because of its lighter weight.
Ford started what would soon become a full-scale transition to aluminum radiators with the Escort/Lynx and Tempo/Topaz. General Motors put aluminum radiators in its then-new front-wheel drive X-cars (Chevy Citation, Pontiac Phoenix, Olds Omega and Buick Skylark). Since then the use of aluminum has steadily grown. Today, Ford uses aluminum radiators in nearly all of its cars and light trucks. General Motors is also using mostly aluminum. Chrysler made the switch with the introduction of its LH-cars (Dodge Intrepid, Chrysler Concord and Eagle Vision), restyled Ram series trucks and latest minivan. Among the Japanese manufacturers, the use of aluminum has also been rapidly expanding with Nissan and Toyota leading the way.
In 1985, only about 24 percent of all new domestic and import vehicles were equipped with aluminum radiators. Today, that percentage is well above 90 percent.
Though copper/brass has been steadily losing ground, a new lightweight "no-flux" brazed copper/brass radiator design may reverse the trend. The International Copper Association has developed this new technology to win back the auto makers with several important advantages. Because copper/brass cools more efficiently than aluminum, a copper/brass radiator can be smaller to reduce weight and space. One new design with a "compact core" dubbed "Cu/Br II" has two rows of fins between tubes and thinner tube walls. The radiator is about 7 percent lighter and 15 percent smaller than an aluminum radiator of comparable cooling capacity.
The new brazing technology for joining the tubes uses a copper/nickel/tin/phosphorus alloy which provides a stronger connection and is more environmentally acceptable than soldering (which uses tin/lead solder). Brazing also means "solder bloom" (a type of corrosion that can form inside soldered copper/brass radiators) won't occur.
The inside and outside of the new brazed copper/brass radiator is
electroplated to give it "unprecedented" corrosion resistance - which is an
essential requirement for all radiators today. The radiator can also be easily
repaired and recycled, the same as other copper/brass radiators (nearly all of
which end up being recycled). Furthermore, the amount of energy needed to
produce one ton of copper from copper ore is only about 40 percent of that
needed to produce aluminum from its ore, so the overall energy picture for
copper/brass is more favorable than that of aluminum.
As the vehicle population continues to age, the percentage of vehicles with aluminum radiators continues to grow, from only about 15 percent in 1988 to about 52 percent in 1997.
During the same period, the overall rate of radiator failures has remained relatively flat, with about 9 million failures a year being the average. Of these, about half are repaired and half are replaced.
According to Modine Manufacturing Company, the average service life of a
typical aluminum radiator today is actually about two to three years longer than
a copper/brass radiator. Consequently, copper/brass radiator failures still
account for the largest share of total radiator repair jobs and replacements.
But the number of aluminum radiators is growing as the population of vehicles
with aluminum radiators expands.
Cooling System Maintenance
The single most important factor that leads to radiator failure is lack of cooling system maintenance. The corrosion inhibitors in conventional antifreeze are gradually depleted over time, so the recommended coolant change interval has traditionally been every two years or 24,000 to 30,000 miles for preventative maintenance. The new long-life antifreeze formulas that can go 5 years or 100,000 miles between changes reduce the need for cooling system maintenance and can reduce the risk of premature radiator failure. But most vehicles still have antifreeze with conventional additives in their cooling systems. So when regular coolant changes are neglected, corrosion goes to work.
Aluminum is more vulnerable to electrolytic corrosion than either copper/brass or cast iron because aluminum is a highly reactive metal. When the corrosion inhibitors are used up and the pH of the coolant drops to 7 or below, aluminum becomes a sacrificial anode and is eaten away.
This same type of corrosion can also occur even when the coolant is in good condition if the engine does not have a good ground connection. Voltage from the charging system will flow through the coolant to ground, creating electrolysis corrosion that attacks the components in the cooling system.
Checking the pH of the coolant with chemically-treated test strips can help you determine if the coolant is overdue for a change. The alkalinity of a typical antifreeze/water mixture will vary depending on the additives in the antifreeze and the ratio of ingredients, but is usually somewhere between 8 and 11. The average for most antifreezes is around 10.5, but when diluted 50/50 with water and added to the cooling system the pH drops to the 8.5 to 9 range. Higher is not necessarily better, though, because some of the new long-life coolants have a pH of only 8.3. Staying power is what counts.
Traditional antifreeze formulas for domestic applications with aluminum radiators, cylinder heads or blocks contain a high level of silicates (which is not really needed in cast iron engines with copper/brass radiators). Silicates form a protective barrier on aluminum that protects the metal. The additives used in European and Asian OEM antifreezes, however, are different. The Europeans use less silicates and rely mostly on borates to inhibit corrosion. Their antifreeze also contains no phosphates because hard water can react with phosphates to form calcium and magnesium sediments. The Asians use phosphates but no borates and low or no silicates because they say borates may actually add to the aluminum corrosion problem if the coolant is neglected. The new long life coolants use an entirely different corrosion inhibiting chemistry that uses carboxylate organic acids instead of the silicates, phosphates or borates. Getting rid of the silicates, some say, helps extend the life of the water pump seal because the microscopic particles of silicate in conventional antifreeze are abrasive.
Regardless of what type of antifreeze you use, it should be meet OEM specifications and be "aluminum-safe" if the radiator is aluminum.
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Larry Carley, Underhood Service, May l997
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