During the early '70s, copper/brass radiators were used worldwide due to their superior ability to conduct heat, but weighed three times that of aluminum radiators, were expensive to manufacture, and experienced high failure rates due to corrosion and stress fractures. Aluminum radiators made their way into automobiles during the '80s, as OEMs embraced the idea of a lighter, more cost-effective design that lasted two to four times longer than copper/brass radiators. Today, the OEM standard radiator-using an aluminum core with plastic tanks-can be found in 99 percent of cars driven on the highway. Follow along as we showcase the ins-and-outs of radiators as we cover what to look for and avoid when addressing your cooling system.
Single-Pass Vs. Dual Pass Radiators
There's been much debate into the theories and logic behind dual-pass/double-pass radiators and their benefits over the more commonly used single-pass system. The Koyo dual-pass radiator (pictured) uses their N-FLO technology that welds two partitions half-way through the radiator core, thus splitting the tank into separate chambers. The "N"-shaped water flow pattern is designed to improve radiator efficiency by passing the fluid over the first half of the radiator and then the second half, allowing the core to dissipate heat twice, while maintaining the coolant in the radiator up to three times longer, offering improved cooling. Koyo representative Scott Oshiro explains, "Dual-pass radiators like the N-FLO were designed specifically for known applications where cooling was an issue, such as with drift cars." In cars being pitched sideways down a track, using a dual-pass radiator allows the radiator to cool efficiently, even when ambient air isn't being forced directly into it at all times. Unless a car suffers from previous overheating issues, all three radiator manufactures we contacted recommended using the traditional down-flow or cross-flow single-pass radiator, which presents all the tubes with the highest possible water temperature at once. Dual-pass radiators work efficiently at high speeds in certain race-prepped systems, but do so at a cost of increased load on an engine's water pump, and inefficient low-speed cooling capacity, which can raise pressure and temperature to higher-than-desired levels.
 Does size really matter? A...  Does size really matter? A larger radiator allows the core to dissipate heat more effectively, but the tube-and-fin design plays just as important a role in the radiator's ability to keep your engine cool. Mike Small of Koyo Cooling Systems explains that as the water is split into multiple tubes, the heat dissipating "load" is split, similar to an 18-wheeler splitting the cargo load over 18 tires rather than four. Radiators using decreased tube pitch (distance from one tube to another) will lead to a denser-capacity core that increases cooling efficiency, but too dense a core will decrease air travel through the fins, decreasing cooling efficiency. The ideal radiator will have optimized fin-density for maximum heat dissipation. "The 'trick' is getting the right balance of fins and tubes based on all the variables," said Small. | 
Single Pass Radiator. |  Internal corrosion can occur...  Internal corrosion can occur almost anywhere in a radiator. This photo showcases a worst-case scenario where the radiator's tubes are fully plugged from rust and sludge. Leak-inhibiting additives or sealers can cause more harm than good, as metallic deposits in "quick-fix" sealants can, over time, block the cooling passages, thus causing overheating. |
 Factory radiators are designed...  Factory radiators are designed to perform well in daily-driven conditions, but commonly fail under strenuous heat cycling and endurance situations. OEM-style radiators using plastic end tanks pressed onto aluminum cores are susceptible to steam erosion and corrosion that can lead to cracking or leaking. |  This Fluidyne radiator cut-away...  This Fluidyne radiator cut-away shows how its internal cooling tubes are designed flat to increase capacity and surface area to aid in efficient cooling. These larger-sized cooling tubes, found on aluminum aftermarket radiators, are less susceptible to corroding and clogging. They use a one- to two-inch or dual one-inch diameter tube (depending on manufacturer specs), compared to a 0.5-inch tube for most OE copper/brass applications. Larger tubing wall thickness helps eliminate ballooning of the core of factory radiators, which is more commonly found on forced induction vehicles experiencing high water pressure. | 
Dual Pass Radiator. |
 Here we see the dissection...  Here we see the dissection of a Koyo R-Series core utilizing a tube pitch of 9.5 mm, representing the peak-to-peak distance between each tube. Notice the striated louvers on each fin? These work as effective heat sinks to catch air as it enters the core to maximize cooling. |  A close-up of this ARC core...  A close-up of this ARC core reveals the smaller, slotted fin design, allowing for air to move faster through the unit, while providing a large cooling surface area for efficiency. ARC Japan says that cooling efficiency does not depend on the thickness of the radiator, but rather the design of the fins and the difference in fin pitch, as shown on this EVO IX radiator using a 1.3-inch-thick core-the same width as the factory radiator. |  |
 Stay tuned for our next issue...  Stay tuned for our next issue as we put four radiators to the ultimate temperature tests, along with details on testing procedure and final analyses. But before we say farewell, here is a teaser dyno plot of one of eight temperature readings we compiled during our grueling 10-hour test session. And guess what? In a head-to-head battle vs. the EVO IX factory radiator, the Koyo radiator lowered engine temperatures by an impressive five degrees Fahrenheit and cylinder head temp by four degrees Fahrenheit. |  |  |