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48mm vs. 53mm radiator

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Old 10-04-17, 02:02 PM
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48mm vs. 53mm radiator

It is time to ditch the ugly Spectra radiator that doesn't actually fit very well. It cools fine, but I desire something shiney and new.


There are two versions of the Koyo radiators for an s4 and I cannot seem to make up my mind. I've read plenty of threads, even those for 3rd gens and I don't see a clear opinion on either side, so I think further discussion is in order... albeit in a rather specific scenario.

My car is an s4 high-compression turbo with a stock front bumper, and I'd like to keep the clutch fan and shroud for simplicity and effectiveness.

I'd like to hear from people who have either radiator and utilize both the stock front bumper and clutch fan/shroud.

In theory, the thicker 53mm koyo racing radiator should offer better cooling ability. I wonder if that is true using a factory stock bumper cover with it's limited air dam size. Is enough air really going to pass through the thicker core for the extra capacity to be of real world use?

The 48mm HH series radiator is a tad smaller, but it might actually work better because of the lesser airflow.

Both appear to be single pass in design.

Discuss.
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Old 10-04-17, 10:44 PM
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If you want to retain the stock fan and shroud, I'd think the thinner version would be better.
Not sure how far you can move the shroud towards the fan before it starts fouling.
The thicker core may help if you're having trouble controlling temps at speed but will definitely be worse at idle/low speed just due to increased resistance through the thicker matrix.
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Old 10-05-17, 04:20 PM
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Originally Posted by clokker View Post
Not sure how far you can move the shroud towards the fan before it starts fouling.

unrelated but sort of related...

i had a strut bar made by a Canadian company that wasn't the best quality and i could not space the bar far enough up and retain threads on the struts without the fan contacting the bar. The options i had were shave the fan (which i didn't want to as i like oem stuff unmodded) or space the fan forward.

I decided to space the fan forward and used about 4 (maybe 5 lol) washers to push it into the shroud more and it does not contact with enough room still to move forward if i didn't run out of stud. if i had to guess it would be spaced about half an inch give or take.

So if the rad is not pushing the shroud much closer i think you may be fine but your experience may vary.
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Old 10-05-17, 09:14 PM
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I can't speak to the cooling efficiency of either rad, but I can comment upon fitment with stock components.

I have an unbranded aluminum eBay rad (I know I know) I am using the stock intake and airbox, the stock shroud, and the stock clutch fan. Picture at the link below:


60 mm depth. For the record it is an S4 N/A. You will have an intercooler to contend with where I don't, but unless you relocate the rad backwards to accomodate it shouldn't make a difference functionally.

First off, the shroud won't mount flush anymore in the stock locations. This is easily fixed by just using speed nuts when practical (in my case, the little mounting tabs on the top and bottom) and securing it with wire when needed (top left and right mount points). Of course if you want to weld to the rad you can make new mount points, but I decided to avoid that. To ensure a proper seal weatherstripping will be required ( I don't have any yet).

Second, the shroud will interfere with the fan itself. The reason is twofold, one is that the shroud is located back and up from where it was (because our rad mounts diagonally), and two is that the shroud might not be mounted flush anymore because you are using custom mounting points. I found that it clipped on the inside where there is a round depression to make space for the stock snorkel. I was able to fix this by sanding on the inside of the shroud to thin it, so it no longer hit the fan.

Third, the stock snorkel won't fit. This is only a problem if you intend to use it (which you probably aren't given you have installed a turbo setup). You can just saw off and seal the baffle on the back of the snorkel to make it fit.

Again, this is a 60mm rad. You may get away with no modification at all.
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Old 10-05-17, 10:41 PM
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I've had a few suggestions to try an ebay rad, but I wouldn't feel too comfortable given the massive turd of negativity I have come across about failures.. I've got to drive this car 1,200miles in four months. Which isn't a lot and I have done it before on FCs in way worse shape on 25 year old stock radiators..but its a comfort zone thing at this point, and Koyo has a good reputation.

Solid info though, good for someone's future use.

Surely someone must have good input on the 48mm HH series or 53mm R series koyos...
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Old 10-06-17, 09:25 AM
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According to the Koyo web site there is only one rad for the S4 HH060642.
Went through a nightmare with my S5 TII and the Koyo company:
https://www.rx7club.com/2nd-generati...anity-1116124/
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Old 10-06-17, 09:43 AM
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The 53mm is an older koyo that is no longer readily available.
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Old 10-07-17, 12:10 PM
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Originally Posted by Acesanugal View Post
Surely someone must have good input on the 48mm HH series or 53mm R series koyos...
i put one in my friends car, and if you need to fit the airbox and stock snork then you want the thinner one. even the 48mm is enough that the stock stuff has to move around and the fan shroud isn't too big of a deal, but the intake is.

so with my 13B-REW, which is FMIC, cone intake, and E fan, i'd do the big one, i've got no stock bits to worry about. my stock T2, i'd do the 48mm one.
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Old 10-07-17, 01:19 PM
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I do run a good size hybrid on mine, and a cone filter because the stock TID does not fit the turbo inlet, so no snorkel to worry about. I want to keep the stock fan and shroud, I'm just a bit worried the 53mm won't allow me that.

Performance is another concern. Keeping the temperature controlled for daily use as well as being able to romp on it quite a bit without the temps climbing up into a less than comfortable range are a must. Do you think I'll have any issues with the 48mm being able to handle this ?
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Old 10-07-17, 01:47 PM
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i'd think either would be ok. with the 48 you might want to spend a minute and seal up any holes/gaps between the bumper and the radiator. i found the foam on top between the radiator and sheetmetal where the hood latch bolts up makes a difference.
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Old 10-07-17, 02:23 PM
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I searched many online stores and made calls but found only one site advertising the R0181. So I purchased a R0181 52mm core Koyo thinking it was old stock and received a 48mm HH060642. Not happy with the false advertising. I think they are all 48mm HH series now. Not polished but dull silver paint.
The core thickness is only 4mm smaller and a few ounces of fluid. Hopefully I won't see a performance difference over my worn out R0181.
Should know in a couple of weeks.
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Old 10-07-17, 02:37 PM
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I'm definitely interested to know how it turns out for you.
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Old 10-12-17, 02:16 PM
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I've veen pouring over all the information I can find.. I feel the 48mm would do better for me, but now my dilemma is this.. do I want the standard koyo hh series single-pass downflow 48mm? Or the 48mm n flo that is a multi-pass?
People seem to go on and on about how the n flo is better, but I have also read some rather intelligent-sounding people say how they do not work well with our waterpump design and that the single pass downflow version provides superior efficiency.

I hate this crap sometimes.. hard to sift through opinion and theory to try and get legitmate answers.

Has anyone had both versions? Let me hear some opinions on n flo vs non n flo.
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Old 10-12-17, 02:57 PM
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The stock rad is right at 1-1/2", 53mm is just barely over 2", the 48mm is a little over1-7/8". Space your shroud out the appropriate amount and then you'll know for sure what fits.
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Old 10-12-17, 03:12 PM
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I'm no longer really concerned about fitment. I've determined that I can modify my shroud to fit either one, my real concern is performance. I daily drive the car and need good performance in normal driving conditions but the efficiency to deal with high speed and high load driving as well.

I'm really leaning towards the hh series 48mm single pass radiator. Seems like it may be the best option, and would not cause increased resistance for the waterpump or higher pressures that hoses won't be fond of.

I like to hear about peoples experiences with either version.
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Old 10-12-17, 06:51 PM
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Originally Posted by Acesanugal View Post
I'm really leaning towards the hh series 48mm single pass radiator. Seems like it may be the best option, and would not cause increased resistance for the waterpump or higher pressures that hoses won't be fond of.
What "higher pressures"?
The system pressure is limited by the rad cap to 13psi, no matter what rad/waterpump/hose combo you choose.
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Old 10-12-17, 07:23 PM
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I've been reading in some 3rd gen threads on the radiator subject that a multi pass radiator can make the waterpump essentially work harder because of the 'barriers' in the rad, which can increase the possibility of belt slippage and it drives the pressure up a bit at high rpm moreso than a standard single pass setup. What are your thoughts on that ?

Obviously no higher than what the cap will let off at, I would think, but higher average ?
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Old 10-13-17, 09:24 PM
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One vote for single-pass.
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Old 10-13-17, 11:00 PM
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Originally Posted by ColinShark View Post
One vote for single-pass.
Thanks man. Have you had both?
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Old 10-31-17, 10:46 AM
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I went with the 48mm HH series and it seems to be working fine. Fitment is perfect in every aspect (aside from me not running the stock airbox or snorkel). Quality bleeder and drain designs. The shroud seals very well to the dimensions of the radiator.
There are no issues with clearance to the swaybar. Seems to be a quality piece !

Next order of business is making sure it doesn't spring a leak... I remember reading something about electrolysis and making sure the aluminum radiator is isolated or grounded? Who's got input on this ?

Last edited by Acesanugal; 10-31-17 at 11:21 AM.
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Old 10-31-17, 11:19 AM
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I have the Koyo dual-pass ("N-flow") radiator on my S5T2. If you could get the dual-pass for the S4, I'd recommend it - couldn't be happier with mine. It basically drops right in, but in the case of an S5T2 installation, you'll need to chuck the stock air intake duct that runs to the air cleaner box, which no longer fits due to thickness of the radiator. The stock radiator shroud & mechanical fan will fit and work just fine with no interference on my S5T2 BUT again due to the thicker radiator, installing & removing the shroud/M-fan gets to be more of a PITA than it was before.

As for the Koyo's cooling performance, with the stock M-fan and all stock fan shroud & plastic underbelly installed, my modded S5T2 (298~303 RWHP) would rarely see temps above 185*F, even on +90*F hot days with the AC running. Also, it basically doubles the coolant capacity (gallons) of the system, which in itself is a big help. I've since done more mods to the car (new ported 13BT, Infinity ECU, more power, etc.), but the same radiator with a 16" E-fan keeps the temps just as cool now.
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Old 11-01-17, 10:25 AM
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Originally Posted by Acesanugal View Post
Next order of business is making sure it doesn't spring a leak... I remember reading something about electrolysis and making sure the aluminum radiator is isolated or grounded? Who's got input on this ?
If you're using the stock brackets, it should be isolated already by those little rubber grommets that isolate the mounting hardware from the metal. Do not ground the radiator.

Basically, distilled water and glycol are great when brand new, but as they age they conduct more. Stray voltage in the engine electrical system can find its way to ground by travelling through the coolant, into the rad, and then into ground (if you have grounded the rad). When this happens, electrolysis begins to eat away at the rad from the inside out. To combat this, make sure existing grounds are healthy, make sure your coolant is healthy and not old (basic maintenance), and make sure your rad does not provide a path to ground. There is also a test somewhere that tells you if you put your multimeter to the DC voltage setting, ground the black probe and stick the red probe into your coolant, there is a certain amount of voltage which is the threshold for concern. I believe it was 0.1V, I'll have to try and find the article I read it from.

EDIT: Here: http://www.griffinrad.com/electrolysis.php?tid=46
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Old 11-01-17, 10:56 AM
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I am using the stock brackets, but if I remember this right, the rubber isolators have a metal bushing that I would think negates the isolating effect. I'd have to look again..

I'll definitely meter it and make sure it's not got current present.
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Old 11-02-17, 12:10 AM
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oh another tip for that is that the PH of the system has to be kind of neutral. any of the Japanese green coolants with distilled water will do this.
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Old 11-02-17, 12:23 AM
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I use mazdas fl-22
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