Anatomy of a Radiator
By Bill Carberry
Radiators are a very important part of your classic car but often get overlooked until they catch your attention with a green puddle or a rising temperature gauge. Most of you know it is there to keep your engine cool but don’t really know how it does its job or how it is made. Let’s consider this a crash course on radiators and how they do what they do.
General Motors used what is called a cellular core design into the late 1950’s. These were also referred to as honeycomb cores for radiators in the 1930’s and older. This is because of the hexagon shape of the air passages through the core. Depending on what manufacturer made the core you could also have diamond shaped cells and various sizes of hex shaped cells. The cellular core that GM started using in the late 1930’s is the same design that was used in heater core material all the way to the late 1980’s when most manufacturers converted to aluminum. A cellular radiator core is actually made from thin copper strip. The strip is run through dies that bend it into a V shape to form the fins or another set of dies to form the tube walls. The ends of the tube walls are folded over and interlocked with the adjoining tube walls to form a mechanical joint. The previously formed fins are inserted between the tubes and it is all placed in a clamp type jig. The fin/tube assembly is then dipped in a vat of molten solder just enough for the solder to wick up about a quarter inch between the separate tube walls and solder them together. It is then flipped over and the other “face” of the core is dipped to complete the process. Replacement cellular core material is made in the specific thickness, height and width needed for the particular radiator.
A tubular radiator is a combination of many components soldered together into one piece. It is composed of copper fins, brass tubes and a copper header. The header is the piece that the tubes go into and the tanks are soldered on to. A header can be basically flat with just a groove for the tank or it can be a dish style header. One example of a radiator with a dished header would be a 1955 to 1957 Thunderbird. The tubes, fins and header are assembled in a jig, dipped or sprayed with flux and then baked in an oven until the solder on the tubes sweats all the parts together. After the core is assembled the tanks are soldered on. If the application for the radiator requires a transmission cooler, the outlet tank will have a cooler installed into it before being soldered to the core. The hose connections (or necks), filler neck and drain plug flange get soldered to the tanks and finally the mounting straps. The finished radiator gets pressure tested much like you would check a tire for a leak. The radiator is plugged with expandable rubber plugs, air pressure is put into the radiator and it is submerged in a test tank. If it bubbles there is a leak that needs attention. Most new and recored radiators are pressure tested to about 18 to 20 psi. Early model radiators might only be tested to 4 or 5 psi if it was originally a no pressure system.
There are several different styles of tubular cores. The most common in passenger cars and light trucks is the serpentine fin design. This is distinguished by the fins being in an accordion or serpentine shape. They “V” back and forth from one end of the core to the other. The face of the tubes is even with the fins. This style was adopted by Ford in the early 1950’s and GM in the late 1950’s. A flat fin style core can be identified by the straight fins that run completely across the core and are perpendicular to the tubes. Each fin is punched out with the tube pattern and creates a very strong core. This is the type of core that Ford used until the late 1940’s. It is still used today in many industrial applications.
Each part has its own purpose. The mounting straps or side brackets are used to prevent the core from bulging apart every time it gets pressurized and are often used to bolt the radiator into the vehicle. The tanks act as a manifold connecting one radiator hose to multiple tubes. The tubes carry the coolant from the radiator inlet tank to the outlet tank and are the first step in getting rid of the heat. As the coolant passes through the tubes the heat from the coolant transfers to the brass tubes. The fins that are soldered to the tubes actually have two jobs. 1) They support the tubes and 2) They dissipate heat. If you have ever looked closely at a conventional radiator you noticed that the tubes are basically flat. If the tubes are not supported while under pressure they would eventually “round out” and close the gaps between them obstructing the airflow. The fins keep the tubes where they are supposed to be and in their original shape. After the heat transfers from the coolant to the tubes it then spreads through the solder joining the tubes to the fins and into the fins. Most radiator fins have louvers to throw off as much heat as possible. This is the final stop for the heat your engine has created as the airflow takes it away.
There is much debate over whether a copper or an aluminum radiator will cool better. There are pros and cons to each material. Copper actually transfers heat better than aluminum. It is easier to repair in most cases than aluminum and until the last couple of years was much less expensive. The drawbacks to a copper radiator are the weight difference (aluminum is much lighter) and the solder joints that hold it together. The solder that secures the tubes to the fins does not transfer heat as quickly as copper and slows down the heat transfer. The presence of solder where the tubes are soldered into the headers is also the main cause of what is known as “solder bloom”. I am sure all of you have looked inside a radiator at some time and observed the white residue growing around the tubes. This growth is the result of chemical reactions from different metals (brass tubes, copper header, lead/tin solder) and lime and other chemicals in the water/antifreeze mixture. Aluminum radiators are welded or “aluminum brazed” and the finished piece is 100% aluminum. This eliminates the dissimilar metals and solder bloom problems that affect copper radiators. Aluminum radiators can also use wider tubes that create more surface area and helps dissipate the heat quicker. Neither has an advantage when it comes to corrosion. Left unprotected, a copper radiator core will turn green and deteriorate rapidly especially in a damp environment. That is why copper radiators have always been painted, usually black. Aluminum will oxidize if not protected from the elements. At Classic Radiator we use Gibbs Brand Penetrant to stop oxidization before it even starts.
A copper radiator can be made more efficient by changing the tube spacing and fin count. The radiators that were made from the 1950’s to the 1970’s generally used ½” wide tubes placed on 9/16” centers from each other. If you counted the fins you might get as few as 6 or 8 fins per inch (FPI). If the tubes are placed closer together and the fins are packed in tighter a denser core is created that throws off much more heat. A high efficiency core can have tubes on 7/16”, 3/8” or even 5/16” centers and fin counts increased to 12 to 14 FPI. That may not seem like a big deal but the surface area is greatly increased. As an example; a 26” wide radiator core with tubes on 9/16” centers has about 45 tubes from side to side. A high efficiency core of the same width has 57 tubes from side to side. Combined with all the additional fins between the tubes this provides approximately 25% to 30% better cooling than the OEM radiator did. A three row high efficiency core will cool about the same as a regular four row without taking away another 5/8” of fan clearance. Going to a thicker core will cool better but there is one big thing to remember. As the air passes through each row of tubes it is picking up heat along the way. The air cools off each following row of tubes a little less than the previous rows. A four row core is of course better than a two row core but increasing a cores thickness does not necessarily mean it will continue to get more efficient as it gets thicker. A core that is too thick will also impede the airflow at low speeds. Griffin Radiator makes most of their radiators with either two rows of 1” tubes or 1 ¼” tubes. They also offer a two row with 1 ½” tubes and a three row 1” tube core but do not recommend it for street vehicles. These cores are designed for high speed driving such as Daytona where you have 175+ mph air going through the grille.
Almost all 1950’s and older radiators are a “downflow” design. This means that the coolant goes into the top tank of the radiator and flows down through the core into the bottom tank and then back into the engine. As car manufacturers went to lower and wider designs this needed to change. “Crossflow” radiators were designed to keep the radiators at the required size but fit within the lower and wider engine compartments. An example of this would be all GM radiators were of the downflow design until Corvette first used a crossflow in 1961. GM took up the crossflow design in many more models starting in 1965. Camaros and Firebirds used the crossflow with their introduction in 1967. The first mass produced Ford crossflow radiator was in 1960 in their full size line.
Putting a brand new or recored radiator in your car will not necessarily keep you running cool if everything else is not at its best. Many older cars came with a 4 blade fan that was barely adequate to pull air through a radiator. Add some horsepower to the engine or air conditioning and a larger fan is definitely required. A 6 blade fan will pull 50% more air than a 4 blade and will not affect the OEM appearance under the hood if you install a stock appearing unit. A fan shroud will also increase the effectiveness of the fan at low speeds by pulling air through all of the core instead of only a portion of it. An auxiliary electric fan can be installed to boost airflow at low speeds and can be turned on manually, with a thermostat or even a pressure switch in the air-conditioning system.
Repairing a copper radiator is something of a specialty that requires special tools and equipment and of course the skills of a “radiatorman”. A proper radiator repair generally starts with the boil-out tank where the radiator is submerged in a bath of caustic acid to remove grease, oil and antifreeze. It will also loosen some of the solder bloom that we discussed earlier. Upon removal it is immediately flushed in the reverse direction of its normal flow. This will push out some or all of the debris that may be clogging the tubes. A boil out will not necessarily remove all of the debris. I compare the debris in a radiator to cement when explaining this problem to my customers. If you have wet cement you can wash it away with a garden hose. Let it dry and it is a whole other story. Reverse flushing your radiator and entire cooling system on a regular basis should prevent the buildup of debris that cannot be removed even by a boil-out tank. After a thorough cleaning the radiator is plugged up at the necks and put into the test tank to find the leak(s). A few normal wear and tear leaks such as a seam leak or minor damage can be easily repaired by soldering. If the core is weak, brittle, has fin rot or is severely damaged or clogged, a replacement should be considered. In some cases we will repair a radiator for a customer but give him a warning that it does not have much life left in it and we cannot guarantee the repair.
Recoring a radiator involves removing the tanks and brackets and replacing the core. Hence the term “Recore”. After removing the tanks and brackets they are glass beaded and soldered on to a new core. During the assembly we will spend the time to reinforce the radiator at its weakest points. Putting extra solder at the corners where the tubes go through the header or even pop riveting the tanks to the headers on certain models will add a lot of strength and life to the radiator. Some people feel that a new radiator is better than a recored radiator. Well, they are wrong and right. If you require as much originality as possible such as OEM part numbers or other stampings then a recore might be your only choice. If your particular radiator is not available as a complete new unit then you would also need to recore. That might mean locating a good set of used tanks and brackets if yours are too far gone. An all new radiator has the advantage of all new components. Being all new does not mean that the quality is as good as you would like. There are some radiator manufacturers that try to sell their product by beating the competition with a low price. In order to provide this low price the quality of the product will usually be compromised. Fortunately there are radiator manufacturers that put quality at the top of their priority list but you must be prepared to pay for that quality.
Servicing your radiator or replacing it should be given the same consideration as you would give your transmission or engine. You should also consider how much you have invested in your drivetrain and protect that investment with a good reliable radiator. When people object to the extra cost of a quality radiator compared to an economy radiator I ask them if they would put a cheap oil pump in their engine.
Cap a Radiator
566 Fulton Street
Farmingdale, NY 11735