Here are some references on radiator thickness vs performance.
Basically, larger is better but thicker is not always better. Thinner is better if but if you can make it larger, then do it. We usually don't have room to make it larger and keep it thin.
Pay attention to the comments on flow rate in the following youtube video. Higher flow rate is better even if the temperature drop is lower across the radiator. More energy is taken out of the system with higher flow rate. When we increase the thickness of the radiator, we slow the flow rate unless we change the pump.
https://www.youtube.com/watch?v=Ldfuzy_JJUo And here is more from another site:
http://www.cliveyboy.com/2012/11/how-to-improve-your-cooling-system/ Radiator
Finally the radiator. This is the most misunderstood part of the cooling system and the one which has the biggest effect should you get it wrong.
Fitting a poorly designed/modified radiator would mean having to greatly increase the air and water flow just to compensate for its inefficiency.
How do we know what is an efficient radiator?
If you fitted two different radiators to your car each of these would try to lose ALL the excess heat (heat load) across its core. In order to do this the radiators need to find a big enough temperature difference between the water and air. Each radiator would allow the water temperature to keep rising until it achieved that temperature difference.
When the radiator has found that temperature difference and is able to lose all the excess heat this is known as its "steady state" condition. A good efficient radiator is able to start losing heat at lower air temperatures and so stabilise (reach steady state) at a lower temperature.
A poor radiator might need such a high temperature to achieve a steady state that it boils before that temperature is reached.
A good efficient radiator is one that can start transferring heat at lower temperatures.
So how do you build an efficient radiator?
An efficient radiator is one that can expose enough water to the air so all the heat is lost at a low temperature.
So if you increase the surface area of the radiator by adding more cores etc you increase efficiency? Not necessarily.
Remember what we said - if you change one thing it always affects one or more other things. In the case of adding a third core you affect both the water and the air. Firstly the water instead of travelling through two cores is now split between three - this means the water slows down. (Remember increased flow = increased cooling).
If the water slows down too much you get "laminar flow", where hot water clings to the tube walls almost stopping heat transfer. N.B. Going to a smaller tube size when adding an additional row is one way to keep the flow rate up, but they are more prone to blocking up.
The air as it travels through the radiator will be warmed up by the first core, warmed up even more by the second core, so by the time it gets to the third core you are trying to cool it with hot air. The temperature difference between the water and air will be much lower. That could mean either little heat transfer or the radiator could start to raise the water temperature to try and increase that difference.
If there is a high enough air flow through the radiator, fitting an extra core may help. But remember, if you add extra cores to a radiator not only do you slow the water down but cool more of that water with hot air. If you are fitting an extra core to a radiator, both air and water flow should be increased for maximum benefit.
A better way is to increase the radiators frontal area either by making it bigger or increasing the number of tubes in the rows. The water flow rate through the tubes will drop (same as adding an extra core) but you have the advantage that more water is being exposed to the coolest air hitting the front of the radiator. Therefore the air will be cooler when it reaches the second row. This helps maintain the temperature difference between the cooling air and the water. The bigger the difference the more efficient the radiator can cool.
A bigger radiator or more tubes per row exposes more water to the coolest air. Again, if you increase the surface area of a radiator, both air and water flow should be increased for maximum benefit.
In conclusion
This should now have covered the major points that affect a cooling system. Hopefully you now understand in more depth how your cooling system works, and so can make an informed decision as to whether that very expensive up rated aluminium radiator with extra cores is actually what you need.
You may also be interested to read an article I wrote on aluminium radiators and how they compare to copper/brass ones.
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