What makes the better Radiator; Aluminum or Copper?
I get asked this question so often that I feel like a broken record telling the pros & cons over and over. I am not a scientist, chemist or engineer but based on my over 32 years of experience in the radiator business here is my opinion on which is better; copper or aluminum radiators.
There is much debate over whether a copper or an aluminum radiator will cool better. There are pros and cons to each material. It has been scientifically proven that 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. In the 1990’s some manufacturers started using a process called “Copubraze” which eliminated the solder between the tubes and the headers. The tubes were brazed instead of soldered which prevented the solder bloom problem and also created a better made core. This process was more costly however and most manufacturers were favoring aluminum anyway due to the weight savings. Copper core manufacturers also started using smaller and thinner tubes to break the coolant down into smaller amounts to further improve cooling. Smaller tubes clogged up much easier especially when the vehicles owner did not adhere to recommended cooling system flushing intervals. They also used thinner material to cut weight and improve heat transfer but the longevity suffered.
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 contact area from the tubes to the fins and helps dissipate the heat quicker. Most aluminum radiators use 1” wide tubes and some manufacturers like Griffin offer 1.25” and 1.5” tubes as well. Traditional copper radiators usually use ½” tubes so a 4 row copper radiator has slightly less fin contact area than a 2 row aluminum core with 1” tubes when you take into account the loss of contact area at the curved ends of the tubes. Most OEM copper radiators were built with the tubes on 9/16” centers from each other. All aluminum cores are built with the tubes on 7/16” or 3/8” centers creating a denser and more efficient core than a standard copper core. I generally tell customers that a high efficiency (tubes on 7/16” or closer centers) copper four row will cool the same as an aluminum core with two rows of 1” tubes. If more cooling is required from the radiator than either of these designs will provide, than an aluminum core with two rows of 1.25” is the thickest recommended for a street application. Any thicker than that and you may have trouble pulling air through the core at low speeds or when at a light.
Aluminum offers the advantage of about 30% to 40% less weight. To a racer this is a huge advantage over copper. Aluminum can also be polished out to a mirror like finish for those concerned with show appearance. 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.
If your radiator needs to be replaced and you want to retain as much originality as possible then recoring your original copper radiator may be the best choice for you. A copper radiator core can be made more efficient by changing the tube spacing and fin count. As I stated earlier 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 had. 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. As I said earlier a core that is too thick will also impede the airflow at low speeds.
So which is better, aluminum or copper? My opinion is neither. Each one has advantages over the other in different areas. The decision over which to use in your particular case comes down to what is more important to you. Weight, appearance, originality and cost all need to be considered before you make your decision. From my own experience on my own vehicles I have found that a properly built high efficiency copper radiator will cool the same as a well made aluminum radiator. Like I said at the beginning, I am not a scientist or an engineer but this is my opinion and I’m stickin’ to it.