Water

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.

Additives

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.

Electrolysis

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.

Repairs

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.