Not All Radiators Are Created Equal

Most people automatically assume that aftermarket radiators are superior or better than OEM or the more expensive units on the market.  Like most things; you generally get what you pay for and higher-end radiators sport superior cooling capabilities while the lesser alternatives generally cool worse than OEM.  We will be looking at photos from two different cores at Verus today, a low-quality unit and a high-quality unit (typically used in all forms of Motorsports) and comparing the two units.  We will only be looking at the cores primarily; as this is where the majority of the heat transfer takes place.  The primary details we will be looking at will be the brazing quality, the tube construction, and the fin construction.

We are pulling from information from past employment where we supplied all forms of motorsports with high-quality cooling components; from IndyCar and F1, to NASCAR, WEC, Trophy Trucks, Sprint Cars and everything in between. 

Core Make Up 

I will be using verbiage that may not be common knowledge for some readers.  Below is a photo with arrows pointing out the three main components that make up a radiator.  They are the header plate, the tubes, and the fins.

Brazing Quality

Brazing is the technique of joining metal together by melting and flowing a filler metal into the joint.  The filler material, called clad, will have a slightly lower melting point than the base metals.  This is how aluminum radiators are constructed; and is a very crucial part of the radiator’s quality and performance.  Brazing radiators is quite a bit more difficult than say, brazing two copper tubes together for a water heater install in your house, but the process is similar.

There are two main braze joints on an aluminum radiator, from the radiator fins to the tubes; and from the tubes to the header plate.  The quality of the actual clad varies as well and can influence both strength and heat transfer.

Tube to Header Plate:

This braze joint dictates the strength and longevity of the radiator.  A good joint here will result in a longer core life.  If this joint leaks, water will begin to leak from the radiator under pressure and the radiator will need to be replaced.  Some very low-end cores are not even brazed here; and are held together with epoxy, which is an inferior way of joining the header plate and the tubes.  All OEM radiators are brazed, high-end radiators are brazed, and some lower-end radiators are brazed or epoxied.

In our case, both cores are brazed.  However, the header plate on the high-quality core is formed significantly to increase the tube to header plate surface area; resulting in a much stronger joint.  The below images both point this out on the high-performance radiator.  OEM and high-performance radiators do this to dramatically increase longevity as the tube to header location is one of the weakest locations on an aluminum radiator core.

Fin to Tube Joint:

This braze joint heavily influences the radiator’s ability to transfer heat; as it joins the fins to the tubes.  As you may have guessed, the tubes carry water (coolant) through them; and the fins transfer heat into the ambient airflow.  Too much clad material and you can reduce the heat transfer; too little and you lose heat transfer again.  To correctly apply the right amount of clad is an expensive process as conditions in the braze process needs to be perfect.  Applying the correct amount of clad also improves the overall strength of the radiator.

In the below photo, I was easily able to pull the tube from the fin joint on the low-quality core.  I could have skinned the tube from the entire fin row if I kept pulling.  I could not separate the tube from the fin on the high-quality core.  I pulled with greater force and less damage occurred.  This is a result of superior clad, brazing quality, and overall better processes.

Tube Construction

Tube construction is important for both cooling and strength.  Material selection varies as does the actual shape/profile of the tube and thicknesses used.  We did not test material selection; but we did do a bit of measuring and comparing.

Initially, you can see that the lower quality core is a twin row vs. a single row for the higher quality core.  This does not necessarily reduce performance but it does increase thickness while not increasing surface area, which is not a positive thing.  The high-quality core is taking advantage of every available mm of space.

Tube Thickness:

Let’s take a look at the dimensions of the tubing itself.  The higher quality core has a tube thickness of 0.1mm, while the lower quality core has a tube thickness of 0.21mm.  This is a massive difference and greatly affects the heat transfer of the core.

Tube Height:

The tube height is also different, ~1.72mm height for the lower quality core and ~1.52mm for the higher quality core.  The higher the tubes, the more blockage on the air side the core sees; however, better water-flow results as well.  The issue here is that with the wall thickness being 0.2mm for the lower quality core; that results in an internal tube height of 1.32mm, the same for both cores.  The higher quality core will have a better air side pressure drop as a result and improved cooling.

Fin Construction

The fins are where the core exchanges heat with the ambient air; and is heavily responsible for both heat transfer and air side pressure drop; both are very important for an efficient and effective heat exchanger.  A lot of time is spent in CFD and wind tunnels to fine tune and improve the individual louvers on the fins to improve cooling.  We will be taking a look at the physical attributes of the fins and explaining how they would affect performance in a radiator.  We’ll look at the fin thickness, the fin heights, and the louver details.

Fin Thickness:

Initially, we can measure the fin thickness.  This is easy to test with micrometers and shows just how different the fins are between the two cores.  This is a massive difference in thickness!  A thicker fin will reduce heat transfer and block more airflow; both negatives if we are after performance.

Fin Heights:

The fin heights are also quite different.  Larger fin heights will allow more airflow through the radiator (reduced pressure drop) but that also means you get less rows of fins and tubes; which negatively impacts cooling overall.  In general, more rows of tubes and fins is better; and due to material costs it generally is more expensive to produce as well.  The below photos show the differences in fin heights; while the second photo shows the difference in number of tubes in a small core section.

Louver Detail:

The individual louvers in the fin, which tabulate and greatly improve heat rejection, are arguably the most important piece of the radiator core for performance.  Performance varies greatly based off this louver angle, the number of louvers, the height of the louvers, etc.  Manufacturing tolerances need to be kept very tight.  We can see in the below photo that the left core, the lower end unit, the louvers are spread apart further, larger, and much fewer.  I count 26 louvers on the lower quality core.  The unit on the right, the higher quality core, has louvers that are much tighter, much smaller, and more densely packed.  I count 30 louvers on the higher quality core.  Keep in mind, the higher quality core is actually thinner as well, so the louvers are much denser.  Also note in the second photo how the louvers on the lower quality core do not extend remotely close to the tube (red arrow) while the high-quality core’s louvers are to the edge of the fin (blue fin); maximizing performance.