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Radiator Construction — Part IV — Tubes

This is the fourth post in a multi-part series here on and to help our friends and customers learn more about their vehicle’s cooling system. The information contained herein, as well as on all of our blog posts, is derived from decades in the cooling system industry. In this post, we will cover serpentine radiator fins. For earlier radiators (honeycomb and cellular), please refer to the first installment in this series and/or check out this chart.


There are three different materials used for making tubes (copper, brass and aluminum) and three methods for making them. Two of those methods have been around for quite a few decades. One is the lockseam tube and the other is the welded or brazed tube. The newest style is called the folded tube.

Tubes for Copper/Brass Radiators

In the early days of the tubular radiator core, manufacturers made round tubes, but as technology progresses, they were able to make the tubes much flatter. The lockseam tube was invented first, but the welded tube came shortly thereafter. At first, the lockseam was the de facto king of the heat transfer jungle, even though the welded tube was at the time – and continues to be – the better product. Both types of tubes perform equally well as far as heat dissipation abilities, but the seamless variety has the distinct advantage of (ahem) not coming apart at the seams and therefore held together better and leaked far less often than their non-welded counterparts. So why did the radiator manufacturers all choose the lockseam? Because of the most obvious reason: it was cheaper. Fortunately for consumers, the superior welded tube became a better value and by the 1970s became the more popular product.

While the flat tube represented an enormous increase in cooling ability, engineers were still able to squeeze out some more cooling from their copper tubes, thus the introduction of the “dimpled” tube. These tubes have divets throughout the tube to slow the coolant, keeping it in the radiator longer and thereby cooling better. Combined with louvered fins (discussed in Part II), radiators were becoming technologically advanced, keeping up with the higher-horsepower engines that were being produced in the muscle cars of the era.

Not until the late seventies and early eighties did the manufacturing process for welded tubes become efficient enough to surpass the lockseams in sales. The welded tubes, now mostly being made of brass, as opposed to the original copper tubes, were finally getting the recognition that they deserved when, suddenly…

Aluminum Cores

…this happened. As we reported in the first installment of this series, the early ‘80s was when aluminum core / plastic tank radiators began to hit the OEM market, and it wouldn’t be long before they became the standard-bearer of the aftermarket, too. While this did bode well for fans of brazed tubes (because aluminum required seamless tubes, so that the headers wouldn’t leak), the influx of aluminum radiators did significant damage to the copper industry. While the vast majority of heavy duty radiators were still made of copper, the passenger car and light truck market is a huge industry and aluminum cores are the industry favorites.

There are essentially two types of radiators that use aluminum cores:

First, there are tabbed header cores. As we mentioned in Part III of this series, tabbed headers have been used on many OEM applications since 1981, with the vast majority sporting aluminum cores. These were implemented to save on fuel mileage due to government standards that all manufacturers have had to abide by for the past four decades. While this was a great development, those same standards are responsible for the Cadillac Cimarron and that is simply unforgiveable. By using an aluminum core and lightweight nylon tanks, manufacturers saved a lot of collective weight over copper and brass, which is heavier, but has better conductivity. Still, these radiators don’t lose as much as you’d think due to the lack of conductivity caused by lead in the solder of copper core radiators. We’ll discuss all of the advantages and disadvantages of both construction types in part VI.

Then there are the all-aluminum radiators. Rather than crimping “plastic” tanks onto the cores, aluminum tanks are brazed onto an aluminum core’s dropseam header. These radiators are used for high-performance vehicles and racing applications

In the early 1980s, several European manufacturers, including Behr and Chausson, successfully experimented with installing “turbulators” in their radiators. Turbulators are flat double-helix shaped inserts that are the entire length of the tube. The turbulator forces the coolant to make more contact with the tube and significantly improves the cooling.

Folded tubes are used on aluminum radiators and only came out in the 21st century. They’re produced by brazing sheet coils in a multi-step roll-forming process – bringing the sheet gradually into the shape of a “B” or a double “B.” Folded tubes have certain advantages – particularly regarding strength. The folded ends of the tube sheet are brazed inside the tube, which creates a very robust bridge between the walls. This results in higher burst pressure resistance. This style of tube for aluminum core radiators has become the favorite of OE manufacturers for its better tube-to-fin contact and greater durability. However, they do leak at times and, unlike many radiator shops, Cap-A Radiator repairs aluminum radiators!

In the next installment, we will discuss the parts of a radiator that aren’t part of the core.

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