Technology changed our cars and not just the old ones either. In fact, the effect technology had on them has probably been the most profound: disc brakes, air conditioning, overdrive transmissions, and fuel injection have made them feel near as new as the latest thing to roll off a showroom floor.

More recently the market has embraced another technological watershed: aluminum radiators—they're light, they're strong, and they're inexpensive. And while aluminum isn't as thermally efficient as copper, a properly built aluminum radiator actually performs within a few negligible percentage points of its copper-brass counterpart. Aluminum even requires the same care and products as their copper-brass counterparts.

But that doesn't make them alike. Aluminum won't forgive neglect … period. The mild neglect that wouldn't faze a copper-brass radiator can wipe out an aluminum one within a week. And for a follow-up punch aluminum radiators aren't as repairable as their traditional alternatives. So pay attention.

Galvanic Corrosion

Dissimilar metals will react with each other if immersed in a solution called electrolyte. In that case the more noble metal will corrode the less noble (base) metal by robbing electrons from it. This passive reaction is called galvanic corrosion and it's the foundation for alkaline batteries.

This isn't a big problem with copper-brass radiators on iron engines because copper and brass are more noble than iron. When electrolytes form in those cooling systems the copper and brass attack the less noble iron. Because the iron is so thick it rarely, if ever, corrodes completely—the coolant usually just turns brown from rust. At worst the corrosion attacks the zinc elements in the radiator joints' solder and cause it to "bloom" or disintegrate, expand, and leak.

Things changed with the introduction of aluminum engine components. Because aluminum is far less noble than copper, brass, and iron it will corrode madly and sometimes completely in the presence of electrolyte. The thin components in aluminum radiators raise the stakes: a nearly imperceptible 1/32-inch-deep pit can poke a hole right through a tube wall.

It should be obvious by now that to protect aluminum radiators we need to prevent the formation of electrolytes. We'll tell you anyway but it's actually no different than what it takes to prevent electrolytes from forming in a cooling system with a copper-brass radiator. But we're going to go a little further and explain a few additional measures. Though we'll reveal them in the context of aluminum these practices are just as relevant to more traditional cooling systems.

To learn the ropes we consulted two experts who have complementary knowledge: Jay Miller and Leon Weidmann. Miller fields technical calls at AFCO Racing, one of the industry's preeminent aluminum-radiator manufacturers. Weidmann owns 112th Street Radiator in Tacoma, Washington, a shop his dad founded in the '60s, one of the few remaining shops that still repairs and re-cores radiators. The guy's seen and probably done it all. Both know what it takes to make a radiator survive.

See the electrolysis damage in this photo? Neither can we but it's there, buried deeply within the core, making an otherwise good radiator impossible to fix for less than a new radiator's cost. It underscores the importance of maintenance.

If designing a radiator mount take a tip from the OEM world and insulate it from the rest of the car with rubber mounts. If the radiator can't complete the electrical circuit to the chassis then the engine can't seek ground through it and wipe it out. Soft mounts also reduce fatigue, a real consideration with aluminum.


Straight water may be the most efficient cooling medium but it's not the best, especially in the presence of aluminum. "Running straight water is one of the biggest mistakes we see people make," Miller says.

Water in an engine is never pure. It picks up minerals from the castings that transform it into an effective electrolyte. The solution is simple: blend the water with antifreeze.

More than alter the coolant's freezing and boiling points, antifreeze prevents coolant from forming electrolytes. The traditional green coolant achieves its corrosion protection with additives like silicates and phosphates. The industry refers to them as Inorganic Additive Technology (IAT).

Though effective for all metals, these silicates and phosphates precipitate from the solution within about two years. That leaves the system vulnerable to electrolyte formation. Worse yet, those deposits hold electrolytes against the radiator walls like a sponge. Weidmann doesn't recommend it but he maintains that the old-style antifreezes will actually work just fine if maintained religiously. "You just have to change it like clockwork," he notes. "Every two years. Any longer and you're asking for trouble."

Extended-Life Antifreeze

Probably because they know people largely neglect their cars and that more vulnerable aluminum components were on the horizon, antifreeze manufacturers developed formulas that use Organic Acid Technology (OAT) to prevent electrolyte formation. These extended-life antifreezes last a lot longer: five years or 150,000 miles. In fact that's what Weidmann and Miller recommend.

But all extended-life antifreezes aren't created equal; some formulas like DEX-COOL use a compound that reportedly attacks silicone and some nylons. Furthermore, DEX-COOL isn't compatible with traditional IAT antifreezes and mixing them can turn coolant to pudding.

"But the other extended-life coolants are great," Weidmann says, and uses them exclusively. "They offer the most protection and they won't fill up (the radiator's) tank with mud," he maintains. As far as recommendations, "I would use whatever the engine manufacturer recommends for the engine," Miller says. "We just recommend a good-quality antifreeze with water." A coolant such as AMSOIL INC. antifreeze is an ideal choice and a mix ratio of 50/50 antifreeze to water is ideal.

Though the manufacturers claim extended-life coolants are good for five years and 150,000 miles, both Miller and Weidmann recommend changing them at shorter intervals. Specifically Weidmann recommends every three years. "When coolant goes bad it turns destructive," Miller adds. "Antifreeze is cheap so why take the chance?"

Consider low-mineral or distilled water mixed with long-life antifreeze an aluminum radiator's primary defense from destructive galvanic corrosion and electrolysis. If possible, choose an antifreeze that advertises compatibility with all types.

Some deem additives redundant in a properly mixed coolant formula but others consider them an extra measure of performance. AMSOIL INC. bills its Dominator Coolant Boost partly by its ability to reduce corrosion when refreshed annually.


Water plays just as critical a role. "Normally tap water is just fine," Miller assures. "The only exception we're aware of are climates with a lot of minerals and impurities in the water. In those cases we recommend running distilled water." Weidmann says, "We use nothing but distilled water—we even distill it ourselves. The system has enough to deal with so why not give it the best possible chance?"

As for ratio our experts' opinions differ. Miller follows the coolant manufacturers' recommendation: 50/50, half water and half antifreeze. Weidmann is a little more conservative: 70 percent water and 30 percent coolant. "We've noticed that even at 50/50 the antifreeze can actually cause damage," he says. "Of course you wouldn't want to do that if you live someplace really cold but even that mixture is good for more than you'd think." (It's good for about 0 degrees F but verify it with a hydrometer for good measure.)

Weidmann maintains that most lethal tube damage results from cramming an oversized radiator in a too-small space. That extra-thick core won't mean a thing if the tubes rub against everything.


We didn't expect consensus regarding additives. Weidmann recommends a specific brand of corrosion inhibitor that has a heat-transfer enhancer. Miller doesn't. "Additives really aren't necessary in a properly designed and maintained cooling system," he continues. "So long as you get good air flowing across an aluminum core the things will work great."

Pay extra for a well-supported core. See how the unsupported tubes belly out toward the side bracket? The tubes were allowed to spread as the radiator heated up and expanded. That imposes huge loads on the tube-to-header joints, an aggravating factor in this radiator's failure.


Cooling systems are also vulnerable to electrolysis, a more destructive cousin of galvanic corrosion. In fact, both dynamics rely on the electrolyte component. Galvanic corrosion occurs passively and somewhat slowly but electrical current actively initiates corrosion. It determines what part corrodes and the rate of destruction. And it can destroy rapidly.

Electrolysis is the consequence of an insufficiently grounded component. Electricity takes the path of least resistance so if an engine has poor grounds and if the coolant contains any electrolytes then the engine will seek ground through the radiator. And because the radiator effectively has a negative charge it will surrender a whole bunch of electrons (corrode).

Since electrolysis relies on stray electrical current we can eliminate it by keeping the electricity on its intended path. And we can do that by eliminating the chassis as a ground path. You see, steel is only about 10 percent as conductive as copper. The limited contact area at the ring terminals compromise flow to a greater degree. Deprived of an easy path through those limited points, the engine will seek ground by every means possible with devastating consequences if the radiator is aluminum.

"The best thing you can do is … take that ground cable and stick it on the tailshaft on the transmission or run it to a bell housing bolt," Rich Fox, at Affordable Street Rods, says. When given an adequate path through a big, free-flowing copper cable then the electricity won't stray. It goes without saying that a strap or cable should ground the chassis and body to the engine, ideally at the same place where the battery ground cable attaches so the connections remain copper to the battery. (Painless Performance offers a ground strap kit that is an ideal component every hot rod should have as part of its wiring that will pay additional dividends.)

The same thing holds true of anything mounted to the radiator. "Absolutely without a doubt it's best to ground the cooling fan to the chassis, engine, or better yet the battery," Miller says. "You don't want anything using the radiator as a grounding point." In fact there's merit to isolating the radiator from the chassis entirely, something that the manufacturers started doing in the '60s by mounting radiators in rubber-padded brackets. Though it's specific to heater cores, Ford's Technical Service Bulletin 06-21-19 states: "…do not ground heater core. If the heater core is grounded, you have provided the electrolysis a path through the heater core. This would cause the heater core to become an anode or receiver and it would promote the electrolysis, or any stray voltage to use the coolant as the ground path." Considering that the radiator is but a giant heater core, the same information applies to it too. Naturally it's impossible to isolate radiators from the chassis and body in very early cars. In those cases the best defense is a strong coolant-service regimen and component-grounding policy, or possibly a less vulnerable copper-brass radiator.

This holds true for copper-brass radiators as well: Don't mount components to the core. The constant heat cycling loosens the ties and the excess lash lets the fan housing rotate just enough to saw through tubes.

Instead, mount fans to the structural elements of the radiator. This is a custom job that partly mounts on a core support but AFCO makes a billet one that's sure to extend the life of any radiator, regardless of its composition.

Material Compatibility

Miller specifies only aluminum fittings in an aluminum radiator. "Other than that you could have a problem," he says. "Normally you can get away with a steel petcock without any issues but anything larger might cause an issue."

And just to state the obvious, fittings on any other part of the car (including the engine) have no effect on the radiator.

This is what Rich Fox meant by grounding the battery to the tailshaft housing or a bellhousing bolt. If given a direct path to the battery, the engine's current won't stray. Ground the chassis and body to this point to minimize the clutter at the battery.


Aluminum, like copper and brass, can be soldered by a formulation unique to the alloy; however that doesn't make solder repairs appropriate to radiators. And their welded construction makes it very difficult to access damage deep within a core. "At times we've cut off part of a corner of the tank and closed off (damaged) tubes and then welded the corner of the tank back on," Miller says. "But say someone hits a rock that goes through one of the tubes. A lot of times there's nothing you can do about that. Those tubes are really thin. If something goes through them usually the game's over. We can't really re-core an aluminum radiator.

"Now if it's small enough we've used this epoxy solder that we stock," he continues. "I repaired the radiator in my Olds five years ago and believe it or not it's still working. If it's done right I think it's effective but really only on small holes and on the core." He recommends TIG welding cracks in the tanks but Don Armstrong at U.S. Radiator noted that tank cracks are often the consequence of fatigue making subsequent cracks more likely.

While all radiators work the same way and benefit from the same maintenance it should be obvious that the aluminum ones require stricter and more controlled adherence to good practice. Ultimately it depends on one's level of commitment: sticklers will benefit from aluminum's weight and cost; slackers, on the other hand, will suffer from its vulnerable nature. And more than offer insight into what it takes to maintain an effective cooling system, knowing the rules helps make the decision to go aluminum a lot easier. Though light, inexpensive, and strong, aluminum isn't for everyone.

Miller calls it an option of last resort exclusively to limp home but he praises the fluid-type sealers to fill pinholes. "Just don't use those pellet-type sealers," he says. "That stuff (goes) right into the water jacket and tanks." He prefers Wynn's but it's tough to find and our local (and trustworthy) parts house heaped praise on Zerex's version.

Should you elect to run flex hose ensure that the metallic component doesn't touch the radiator. That represents a direct path for the engine to seek ground through the radiator regardless of antifreeze or grounding integrity. The same holds true for the wire support in rubber flex hose. This one touched the water neck and the radiator, hence the powdered rust.

Introduce a metal to the cooling system that's less noble than the other critical metals and it will take the brunt of galvanic corrosion. Marine shops sell these zinc pencil anodes in brass NPT plugs for less than $5. Replace the petcock with one of the 1/4-inch jobbies. Technically mixing brass with aluminum is bad but a galvanic reaction can't exist there so long as the zinc stays intact. Note that these won't control electrolysis.

Test your coolant's pH level with litmus strips. A pH lower than about 8.5 indicates an excessively acidic mixture and an environment rich in electrolyte. Consider this worthy of a flush and refill with fresh coolant.

Consider an adequate overflow container mandatory. If exposed to air when hot the protective elements in even the best coolant will form solid deposits. That blocks tubes and compromises the coolant's ability to prevent electrolytes from forming.

925 Tower Ave.
WI  54880
AFCO Racing Products
P.O. Box 548
IN  47601
Painless Performance Products
2501 Ludelle Street
Ft. Worth
TX  76105
US Radiator
4423 District Blvd.
CA  90058
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