CSF Race On Your Cooling Questions
Keeping Your Cool

A few weeks ago we gave you the opportunity to ask the experts at CSF any burning questions you had on automotive cooling. As usual, there were some great questions asked, and Ravi Dolwani – head of CSF’s dedicated Racing & High Performance Division – has come back with some detailed answers that anyone looking to upgrade their vehicle’s radiator – or seek extra performance from their cooling system – should definitely read.

Let’s get into it…


What’s the performance difference between a horizontal and a vertically cored radiator? Also, can you use a small, thicker radiator instead of large thin one?

Ravi Dolwani: This is a two-part question so let’s start off by discussing the correct terminology for these types of cores. A horizontally cored radiator is called a cross-flow radiator and a vertically cored radiator is called a down-flow radiator. There is no difference in these radiators if all variables remain the same. Vehicle manufactures select the type of radiator core they will use on a specific application based on their space restrictions (length and height) as well as their desired placement of inlet and outlet connections. If a radiator is a down-flow type, but is longer (length) than it is taller (height), then changing the design to a cross-flow type will most likely have a positive affect on the performance of the radiator. Although coolant will not move through the cooling system as quickly, the outlet temperatures can be decreased because heat dissipation is improved by lengthening the coolant path from side to side, which more effectively transfers excess heat from coolant to air before leaving the radiator.

For the second part of the question, let’s start by understanding how a radiator works. The most important aspect of proper engine cooling are the three variables specific to each vehicle that work together in harmony to combine for a perfect cooling system; surface area contact, cooling capacity, and flow (water as well as air (entry and exit]) A large thin radiator will have more surface area contact between the air flowing through the system and the aluminum material of the radiator used for heat exchange (tubes and fins). This thin radiator will also have less heat soak potential than the small thick radiator. Without knowing all the variables, it is hard to give a definitive answer, but I would recommend always looking to achieve better surface area contact before resorting to larger cooling capacity.


Regarding radiators specifically, though I suppose it should translate to any air-to-liquid cooler; how important is shrouding, both before, in between, and after individually cooling components?

RD: Shrouding is extremely important and essential to proper cooling as air follows the path of least resistance. Having a shroud (or air duct) in front of the cooling system will help create a ‘tunnel effect’ and force air directly into the cooling system. Having an efficient fan shroud at the back of the cooling system will help the fan pull as much air as possible through the core and out of the cooling system. Ducting is especially important with low speeds and/or indirect airflow, similar to what vehicles experience during drifting. The photo above of the Bergenholtz Racing Mazda RX-8 Formula Drift car demonstrates the use of a custom sealed-off shroud to force air over the v-mount radiator core.


How important is engine bay venting, as it relates to airflow through traditional placed front of engine radiators?

RD: One of the three main variables of cooling is flow. This question pertains to the flow of air. A well-balanced and efficient cooling system needs air to flow unobstructed through (entry) and out (exit) of the cooling system as quickly as possible. Venting becomes more important in engine setups where the back of the fan (or just radiator if no fan is installed) is up against the engine block. This setup creates a ‘wall effect’ and causes the air to stagnate having nowhere to travel to. Adding hood vents allows hot air to better escape the engine bay, which will help reduce engine temperatures.

A perfect example of proper placement of the radiator within the engine bay combined with venting is what we experienced with Formula D champion Michael Essa in 2010 with his BMW E92 M3. After moving his radiator up as much as possible to the nose of his car away from the engine block, he was able to reduce his temperatures 20 degrees (Fahrenheit). He had great entry flow as well as proper exit flow with plenty of space for the air to travel through the system and out of the vents installed in his hood.


How are you different from the cheap china made cores? Do you guys use higher tier china made cores?

RD: CSF manufactures its own cores using JIS 3003 Spec minimum aluminum material, none of which are made in China. Most radiator manufactures do not manufacture their own cores, and this is the portion of the radiator that is most commonly outsourced. This is also the most important part of the radiator as this is where all the heat transfer takes place.


There are two components of a radiator core which are brazed together, tubes and fins. In regards to tubes, CSF uses a special tube called a ‘B-tube’. Unlike a regular oval shape ‘O’ type radiator tube, CSF uses a specially engineered tube in a shape of a ‘B’. These B-tubes are carefully formed and then brazed over the seam to seal. CSF is able to use thinner and lighter aluminum material for better cooling efficiency and weight savings because this design is actually stronger than normal O shape tubes that are welded. The design (inlet in the middle of tube that is seam brazed) increases the heat transfer surface area of the tube by approximately 15 percent over regular tubes. With B-tubes you are able to get ‘dual liquid laminar flow’. The tubes are made from special clad aluminum and are intricately formed on our high precision six-stage tube-forming mill. No other aftermarket radiator manufacturer uses this technology.


As for fins, in our high performance applications, CSF uses a multi-louvered, serpentine designed, aluminum fin to dissipate the air as much as possible over the surface area of the core for better heat transfer efficiency. We have several different configurations of fin heights, widths, and pitches to allow us to test and maximize the efficiency per individual application on our in-house wind tunnel machine. We also have several different types of fins for other applications such as industrial or agricultural which require non-louvered fins.

Heat Is The Enemy

How important is a shroud for radiator performance?  I’ve had cars with factory single row rads, no shroud and a clutch fan that cool better than my dual/tri cores with e-fans (especially at idle). I feel like no shroud e-fan versus clutch fan shouldn’t make a difference, but I guess I just want to know if there’s a way to match your engine to radiator/fan setups? Shroud or no shroud? Mounting an e-fan on the ‘front’ or engine side of the radiator for performance? And how cool is too cool? How do I size the combo to adequately cool my engine without spending money on unnecessary or overly excessive hardware?

RD: A fan placed in the front of the radiator is called a ‘push fan’ and a fan placed behind the radiator is called a ‘pull fan’. Generally speaking, due to space restrictions and the concept of staking multiple coolers in front of the radiator (i.e condenser, intercooler, oil cooler, etc), it is generally very hard to incorporate a push fan set-up. Most of the time a pull fan set-up is the preferred method.  Secondly, a pulley-driven fan uses some of the engine horsepower to operate, where as an e-fan uses the electricity generated by the alternator. An e-fan reduces the load on the engine. Thirdly, in order to properly size the fans needed for a specific engine bay set-up, you must first understand the set-up of coolers and use of the vehicle. For example, if your car is a dedicated track vehicle that is always traveling at high speeds, then proper ducting (shroud) is more important than the type of fans used as air will always be constantly traveling through the system at high speeds. In comparison, if multiple coolers are being stacked together in a daily driver with a small front grill then a high CFM rated fan set-up will be crucial for proper cooling, as you will need to pull lots of fresh air through the cooling system at all times, even at idle, especially if the vehicle is located in a hot/humid region of the world. Every vehicle has a specific optimal operating temperature. It’s up to the thermostat to regulate this temperature and for the cooling system to perform well enough to achieve this desired level for optimal performance.


At what point does a factory radiator need to be upgraded to an aftermarket performance aluminum one? I have a Lancer Evolution VII with a few mods that doesn’t seem to have any problem with cooling with the stock radiator, so what benefits (if any) would I get from upgrading it?

RD: If your vehicle has its temperatures under control then the biggest benefit that you will gain from upgrading to an all-aluminum design by a quality manufacture is the reliability of the stronger aluminum end tanks and high burst pressure capabilities. Every product has its life cycle, and generally speaking, plastic end tanks of OEM radiators usually crack around the five to nine-year mark – especially if proper maintenance isn’t regularly performed. Other benefits could be weight savings and aesthetics of a hand-welded aluminum radiator.


Is CSF planning on releasing aftermarket radiators for popular old school Japanese performance cars?

RD: As you are all aware, no manufacturer can make an application for every single model. There are other well know and respected high performance radiator manufactures catering to this ‘old school’ Japanese performance market. Currently CSF is focused on developing new applications for Porsche and BMW as well as venturing into ultra premium platforms like Lamborghini and Ferrari (coming soon!). We are also developing coolers for Yamaha motorcycles. The objective of CSF’s High Performance Division is to push the boundaries of automotive cooling. If you have an idea that you think there is significant demand for, let us know!


I have been thinking of buying a cheap aluminum radiator off ebay for my 240SX. Surely this has got to work better than my old OE one?

RD: Your stock radiator will work better than any eBay radiator or lower quality brand high performance radiator. If you are looking for something cheap and shinny to look good next time your hood is popped open then I guess it will ‘work’ better than stock. As far as performance and reliability, radiators are like everything else in this world; you get what you pay for. This is the #1 question I get asked. Do yourself a favor, and research the technology and manufacturing process going into the cooling system. If the manufacture is not touting these parts of the their product, then it’s probably just another private labeled eBay radiator which you are paying a marketing premium for. I’ve had the privilege of walking through over 50 radiator factories across the world from some of the highest end in Germany to back alley, off shore types. It’s amazing how many factories are simply spray painting logos on cores for different manufactures. Do your research and become an informed buyer!


Performance is a very broad topic covering cooling capacity and a host of other measurable characteristics. How does weight factor into your designs? I’m sure it is measured and minimized, but do you have any sort of Q/lb requirement your designs must meet? Do you measure ‘performance’ by any standards other than cooling capacity and reliability?

RD: At CSF weight is a huge factor in our designs that, in my opinion, is often overlooked by other manufactures. One of the mottos of our Racing & High Performance Division is ‘Thin is in’. Because of our core manufacturing technologies, we can achieve the same performance from a one or two-row radiator core that our competitors claim they achieve because they have a huge three or four-row core. Our slim designed radiators are better not only for entry and exit airflow, they are also better at avoiding heat soak. This design philosophy comes with huge weight savings in the amount of aluminum material not needed as well as the weight saving of coolant volume that is no longer needed in the system. Combined with our lightweight B-tube technology, CSF’s all-aluminum radiators are either lighter, equal in weight, or extremely close to the OEM plastic/aluminum radiator weight. For example, we just measured our new Porsche turbo radiators against stock, and they both weighed 8lbs (3.6kg). Ours being an all-aluminum two-row version with 20 percent better cooling efficiency versus the plastic/aluminum single row radiator. We are targeting the highest levels of motorsports and serious enthusiast so every ounce counts to us when designing. We measure performance several different ways, but the biggest test is what the cooling system does on the track in real life racing conditions. In the lab, we measure life cycle testing, vibration testing, thermal cycle, and burst pressure testing.

Thanks to Ravi Dolwani at CSF for his expert insight and of course you guys for all the great questions.



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Great read. Thanks for selecting my question! (the last one)


I really liked the section on types of flow and radiators. I've been wondering about that for years!


True about the weight. I removed my old aluminum radiator (name-brand too) and replaced it with CSF. Not only was the CSF bigger, wider, taller and thicker, but it was significantly lighter too! Dropped an extra 2-3 degrees Celsius at idle with a/c on, 3-5 with a/c off


Thanks Ravi. A very informative read.

BiTurbo from oppo

Drat, missed the question session.

Should be a quick one, which is preferable for a fan setup? A push-fan, or a pull-fan?


RodChong Thanks for the oppertunity Rod.. BTW - Reading "Maximum City" when I have the chance. really enjoying it!


BiTurbo from oppo Best case scneneraio would be to have both if possible, if not - go with pull fan


I should have asked , how is the strength of the thinner radiator. Will a bug put a dent to it , if it is hit. 

Too bad they dont make one for the bnr32 >_<.

BiTurbo from oppo

CSFrace Excellent :) thanks man


Great write up !!
Theres one question left i would like to ask:
is it possible to run air to air  intercooler core units to cool the engine coolant fluid down ? these cores appear thicker n less ristricted & feature thicker tins to ensure better cooling.

i just never saw someone abusing them for that kind of purpose :(

some say: larger fins would offer superior flow n less ristriction. Others say:  ristriction is the key to cool the cooland down.

please help :)


Thanks :)


Ask the Expert is so awesome. Great article


I liked when you mentioned that "shrouding" can improve the performance of the radiator and the cooling system.  It would make sense, because if the shroud is forcing air into the system, then it might work more efficiently.  The other part that caught my attention was when you mentioned that you get what you pay for, so purchasing a higher-priced radiator might not be a bad idea depending on the situation. http://www.aersltd.com/en/radiators.html


i am using a 250cc cbr bike  engine in a formula type car for my project, so i want to know that if i change the radiator with the bigger one will it effect the performance of the engine .A change in length of pipes from engine to radiator and back change the cooling potential of radiator.


mayur darade The question you are asking is slightly ambigous.. Here is what I can answer for you with the information that you have given. 
1) Are you running hot now? Do you have a thermostat regulating the engine temperature? Do you have a fan running on the radiator?
- If you are not running hot, and are running in an optimal temperature range, then changing the radiator will not be neccesary. It will actually just add weight to the vehicle. 
- If you are running hot, then yes it will help provided that it is set up correctly.. Longer pipes to and back from the engine block creates more pressure drop. Make sure that the water pump you are using is creating enough pressure flow to run the system correctly (Also the bigger radiator will create more pressure drop as well). 

Hope that this helps!


Is there any explanation as to why there would be a ~25psi pressure drop when the CSF radiator with the liquid to liquid oil cooler is installed.

I have a built WRX and recently had the new 'O' line CSF rad with oil cooler installed and under load the oil pressure dropped from 600 kPa (90psi) to 400 kPa (60 psi).