Radiator Construction — Part I – Core Styles

This is the first post in a four-part series here on CapARadiator.com and ClassicRadiator.com to help our 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 of experience in the cooling system industry.

In the early days of the automotive industry, that being the late 19th century into the early part of the 20th century, passenger cars and trucks had about as many different styles of radiators as they did methods of getting the wheels to turn. And while manufacturers toyed around with gasoline, diesel, steam, electric and even hybrids (well, Porsche did), they were also experimenting with different modes to cool those engines. Most radiators of the time were astonishingly complex creations.

Honeycomb Cores

The design that became most prevalent was the honeycomb core radiator, which was invented by Wilhelm Maybach and patented in 1900. Prior to the 1920s invention of the water pump, all radiators were gravity-fed. Honeycomb radiators were made up of hundreds of little hexagonal tubes that were normally 2” to 3” in length and bonded together in the front and back, leaving a gap between the tubes, but only inside the core. The coolant would get heated inside the engine, which led to expansion of the liquid. This would cause it to trickle to the top of the radiator, which was always the highest point of the cooling system. The coolant would then cascade down through the copper tubes, and the ambient air would blow through the radiator, dissipating the heat. Eventually, the coolant would find its way to the lower radiator hose and back into the engine at a lower temperature.

Cellular cores

Fortunately, other methods of radiator construction were developed by the time that water pumps and pressurized radiator caps were invented. The design that successfully replaced the honeycomb was the cellular core. It wasn’t that great, but it was significantly better than the honeycomb. Unlike modern radiators, cellular cores have no separate tubes. The passageways are formed during the manufacturing process by pulling the copper material through a series of dies & rollers. Cellular cores were at the top of the radiator food chain from the 1930s until the mid–1950s, when the tube-and-fin design began to dominate the market. They were also the top dogs in the heater core sector through the 1980s, when they were overtaken by tubular aluminum heaters.

Tube-and-Fin Cores

In the 1930s, some radiator manufacturers began designing their cores with copper tube-and-fin radiator cores and brass tanks on the end. This design, although modified tremendously over the past decades, is essentially the concept behind all radiators currently being made, including aluminum core radiators and heaters. There are several different configurations nowadays including:

  • Aluminum

  • Copper/Brass with serpentine (aka corrugated) fins, using multiple spacing patterns

  • Copper/Brass Flat Fin with multiple tube sizes and patterns

Flat Fin Cores

The flat fin design was the first tubular radiator to hit the market. While these fins were great for strength, they were also extremely heavy and didn’t provide terrific cooling. Still, it was an improvement and many semi-trucks are still made with them today. Although the copper industry has found ways to make their products lighter, these radiators are still very heavy and for that reason, Cap-A Radiator (one of the very first shops ever certified by NARSA as Heavy Duty Specialists) has installed a system in our new shop to make it much easier to service and recore heavy duty industrial radiators

Serpentine Cores

It wasn’t much longer before the car and light truck industry replaced their flat fin radiators with the serpentine design that you will see on the vast majority of late-model car and light truck radiators. In fact, this design is such an improvement over the older designs that they are also found on many earlier radiators that needed to be recored. While the basic design arrived on the scene in the 1950s, the high efficiency (HE) setup followed in the 1970s. To create the HE design, engineers started making the tubes smaller and more closely packed together. Most HE cores have 5/16” tubes on 3/8” centers or 3/8” tubes on 7/16” centers. By comparison, standard tubes are generally 1/2” tubes on 9/16” centers. There are multiple advantages to the HE core. One is that more of the coolant stays in contact with the tubes. Another advantage is that by having the tubes closer together, there are about 20-25% more tubes on average. The HE configuration does have one drawback, in that the smaller tubes clog more rapidly than a core with larger tubes. However, they are such a significant improvement over the standard design that replacements of flat fin / cellular / honeycomb radiator for improved cooling will always be either a high efficiency radiator or an all-aluminum one.

Aluminum Cores

By the early 1980s, most original equipment manufacturers began putting plastic tank radiators in their cars, light trucks, and even heavy trucks and buses. This configuration took hold during the 1980s in order to lower vehicle weight and subsequently get better fuel mileage. Whereas most major manufacturers, including Ford, GM, Mazda, Nissan and all of the German companies went with aluminum cores, a few stuck with copper cores at the beginning; this included Chrysler, Toyota and Honda. However all three of those companies have since joined with the others in using aluminum cores for their products.

Today, the majority of radiators in passenger cars, light trucks and vans are constructed of aluminum cores with plastic tanks. In heavy duty and industrial applications, the radiators of choice are more often copper cores bolted on to steel tanks or soldered to brass tanks, although there are still copper/plastic tank HD radiators as well as aluminum core/plastic tank combinations being built today by some OE truck manufacturers.

Up Next…

In Part II, we will discuss the design of tube–and–fin radiators. Stay tuned!

This information is courtesy of Cap-A Radiator and its subsidiary, Classic Radiator. 516-293-9026

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