Falling For The Three Row Gimmick

In our last post, we covered copper brass radiators and compared them with aluminum. We left off by comparing the thermal conductivity of aluminum with copper/brass. Copper/brass has almost twice the thermal conductivity of aluminum. Yet, aluminum radiators can transfer a lot more heat than their copper/brass counterparts and keep your engine running a lot cooler.

So how in the world can this be?

Aluminum is a much stronger material than copper, which is what gives aluminum a huge edge in keeping your engine running cooler. Why the strength matters comes down to the radiator tube size. Aluminum radiators are typically made with 1”, 1-¼”, 1-½” and 2” cooling tubes. Copper/brass radiators are typically made with ⅜”, ½” or ⅝” cooling tubes.

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As you can see, aluminum radiators are made with much larger cooling tubes. These larger cooling tubes are the reason why aluminum cools better. And the reason aluminum radiators use larger tubes is because aluminum is stronger. If we tried to make a copper/brass radiator with 1” tubes, the tubes would burst because they can’t handle the pressure. That’s why the largest cooling tubes use in copper/brass radiators are ⅝”. With aluminum radiators, cooling tubes can be made up to 2” in size. That’s a 3.5 fold difference.

Why does size matter?

Like in many areas of life, size does matter. Let’s compare two radiators. The first is a copper/brass radiator with 3-rows of ⅝” tubes. Doing some simple math, the total cooling surface area is 3 x ⅝” or 1-⅞” total of cooling surface area. To put it in decimal, 1.88” of surface area.

The second radiator in our comparison is a 2-row aluminum radiator with 1” tubes. Doing some math again, and thankfully if math isn’t your thing, this math is simple: 2 x 1” = 2.0” of cooler surface area.

So the aluminum radiator has a slight edge over the copper/brass radiator in terms of surface area. Yet the copper/brass has a huge lead over the aluminum in thermal conductivity. Which might lead you to believe there is something else at play that gives aluminum an advantage over copper/brass. And you are correct.

The main reason aluminum performs so much better than copper/brass is tube gaps. Tube gaps are the spaces between the tubes in the radiator core. Because copper is weaker than aluminum, copper requires larger tube gaps in the radiator. This is because if the wall thickness in the header is too thin, the header will crack. On copper/brass radiators, the tube gaps are typically ⅜”. Yet on aluminum radiators, the tube gap is only ¼”.

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These tube gaps are hugely restrictive to airflow across the radiator core. They are like giant speed bumps that slow the air down and cause higher pressure drops across the radiator core as air flows across it. How does this affect your cooling?

Well, it’s quite simple. Let’s say you have a 2500 CFM 16” electric cooling fans. When cooling fans are rated for CFM, they are rated with what’s called a no-load condition. That means if you held the fan up in the air with no restriction in front of it, it would move 2500 CFM. Yet when you bolt it on to a radiator, it’s going to move a lot less air because it now has to pull air through the radiator core.

This 2500 CFM fan bolted to the 3-row copper/brass core might only move 1100 CFM of cooling air. Yet the same cooling fan bolted to our 2-row aluminum radiator might flow 1700 CFM, even though the core is thicker than the copper/brass radiator. How can that be?

It’s because of the tube gaps. Tube gaps make a HUGE difference in airflow of a radiator core. The fewer and smaller the tube gaps, the better the core will flow. You can see the aluminum has only 1 tube gap whereas the copper/brass radiator has 2 tube gaps. This difference in tube gaps is what gives aluminum a HUGE advantage in keeping your engine cool.

There are also a few other reasons that give aluminum a significant advantage over copper/brass radiators.. Since aluminum is a stronger and lighter material, this affects how dense the cooling fins can be. If the core becomes too heavy because of the weight, the fins at the bottom of the radiator can collapse because they can’t handle the weight of the radiator.

This is where aluminum has a triple advantage. Not only is it stronger, it’s also lighter. Which means the fins can be made with thinner material while still keeping the structurally core radiator strong. Thinner material results in much more efficient heat transfer. And since the material is much lighter, that means we can crank up the number of fins in the core without causing the fins at the bottom to collapse from the weight above it.

By the way, I don’t recommend handling electric fans that are not mounted to a shroud. You may think electric fans are not powerful enough to do harm, yet they are extremely powerful and need to be handled with care. I speak from experience since I lost ½” of one of my fingertips testing fans! Electric fans can be extremely powerful and need to be handled with care.

So in the next e-mail, we will tie it all together and how you how just like snake oil companies came in and sold snake oil 4-row copper/brass radiators, they have now moved into selling snake oil 3-row aluminum radiators.

Copper Brass Radiators Versus Aluminum Radiators

Back in the day, if you needed a new radiator for your hot rod, your buddy probably said:

“Just get yourself a good 4-row”

Before aluminum radiators were around, the only upgrade from a factory 3-row radiator was either a 3-row high efficiency model or a 4-row. A 4-row added another row of cooling tubes which provided approximately an extra 20% of cooling power over a 3-row. Back 30 years ago, you could roll down to your corner radiator shop and even have him ‘recore’ your factory radiator with an upgraded 4-row core.

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However like many thing in life, not all 4-row radiators are made the same. Back in the day, there were snake oil radiator companies that made cheap 4-rows. One way they accomplished this was by using tall fin heights and smaller tubes. A good 4-row radiator would have 4-rows of ⅝” tubes where as a cheap model would have 4-rows of ⅜” tubes.

These snake oil companies took advantage of most people’s ignorance and sold them a cheap 4-row that wasn’t likely to cool any better than the 3-row they had. Infact, in many cases, it might even cool worse.

Fast forward from the 1970s to the 1980s. Fuel economy is now becoming important and car manufacturers are looking for ways to make lighter cars. Switch the radiator from a copper/brass to aluminum model can save 10-20 lbs in many cars. For us hot rodders, weight is bad. So ditching the copper brass radiator for an aluminum model is a no brainer.

There are many old wives tales about why aluminum radiators cool better. The most common one is ‘aluminum dissipates heat faster than copper’, which isn’t true at all. Copper is an excellent thermal conductor. In fact, copper has almost twice the thermal conductivity of aluminum.

Yet, despite having a much lower thermal conductivity, aluminum radiators can transfer a lot more heat away than their copper/brass counterparts. You many be wondering how in the world that can be? It’s a great question with a simple answer, which we will explain in our next e-mail. Watch your inbox for the next few days.