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Radiator Construction — Part III — Headers

This is the third 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 radiator fins.


And while we would like to move to the other main part of the tube-&-fin core, the tubes, we first need to explain what a header is. That’s because tubes are the coolant-carrying channels that run from the inlet header to the outlet header. The header connects the tubes to the tanks and is a (usually) rectangular plate, although many earlier models, and Fords in particular, didn’t conform to this particular rule-of-thumb. They often had diamond shaped headers and, for more than thirty years, “bucket” headers on many downflow radiators.

The bucket design is most easily explained using a visual, such as the one above. Here we are about to replace a bucket header core, similar to the core on the left, with the right-side core, which has a standard “dropseam” header. We also had to build a new brass tank for this project, as the original flat tank is a completely different design than what is required for the dropseam core. As you can tell by this picture, the tubes in the standard core are longer and this means that it will cool better. The diamond shaped header also allowed for more coolant to be in the top tank of the radiator, but didn’t cut down on the length of the tubes, as the bucket header did. The biggest detriment with these radiators was that, as engine compartments became tighter, there was no longer enough room to fit them.

Headerless Radiator Cores

Early radiators (cellular and honeycomb) had no header at all. The cores were soldered directly to the tanks. Rather than a lip that goes straight down into a dropseam header, the lips on these OE tanks turns 90° inward or outward, making it impossible to replace the original with a modern HE core. There are, of course, solutions. We’re Classic Radiator, after all, and this is our specialty. In fact, we have three solutions!

First, if the owner is looking to preserve the vehicle exactly as it came from the factory, we can install an exact duplicate of the core, even if that means a honeycomb core with crazy header sizes and a crank hole in the middle of the core! This solution is only good if you’re not increasing the power of the car and is best used for a completely stock restoration.

However, if you’re installing a performance engine, this solution isn’t for you. The easy way out would be to install a high-quality two-row aluminum radiator if available. Pro Tip: Unlike copper/brass radiators, where more rows equal more cooling, two-row aluminum radiators usually cool better than three- or four-row cores! They actually have more tube-to-fin contact and we’ll delve into this subject in Part VI of this series!

Most often, the best solution is to have us recore the radiator. For best-in-class cooling performance, we can create a high efficiency copper core. There are two ways to do this. If the lips of the tanks turn outward, we can install a core with a “foldover” header. As the name implies, it folds over the lip of the tank before we solder them together. If the lips don’t turn outward, we can have the core made with a box header, such as the one in this picture, and then solder it directly to both tanks.

Tabbed Headers

Tabbed headers are used on the majority of plastic tank radiators. As seen in the picture below, tabbed headers have dozens of tabs. The tabs are folded over a nylon-based tank (commonly referred to as a “plastic tank”) on both sides for a crossflow radiator or at the top and bottom for a downflow radiator. Between the header and the tank is a gasket made of EPDM rubber. When the tabs are folded over the tanks, the rubber gasket compresses and creates the seal between the two parts.

Behr, an OEM supplier for Porsche, VW, Audi, Mercedes and BMW, still makes some, but not all, of their aluminum-core radiators with a “ribbon header,” also called a “ripple header.” This type of assembly requires special tools to assemble and to repair. These radiators, which were never very common before, are extremely rare these days.

There used to be one other type of header for some copper core plastic tank radiators, but they’ve mostly faded into history. In the early days of PTRs, some suppliers (most notably Toyo and Nippondenso) for Toyota, Honda, Renault and DeLorean made their cores without tabs, and held everything together using U-shaped “crimp strips,” which were two separate pieces that went under the header and would get crimped over the tank. This experiment didn’t last long, as cores just never held together very well and those manufacturers soon turned primarily to aluminum core radiators. Modine Corporation also used a similar, but significantly better setup for some Ford heavy duty radiators in the 1980s and 1990s.

Bolt-On Headers

The last type of header that we’re going to discuss is the bolt-on header. For decades, the companies that manufacture radiators for semis, buses and heavy equipment have been building radiators with bolt-on tanks. Most of these radiators are made of flat-fin copper cores with steel tanks, although some have steel cores and fins, also, and a few even have brass tanks. Because steel can’t be easily soldered or welded, the bolt-on header was invented for these heavy duty applications. When being assembled, a cork gasket is placed between the header and the tank to seal it from leaks. These radiators are very strong, which is important because of the vibrations of a diesel truck, bit they are also very heavy and not practical for automotive use. Cap-A Radiator is experienced in working with these massive radiators and fully prepared to work on the vast majority of them!

In the

next installment of this series, we’ll learn about both copper and aluminum cores.

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