nah not anymore i was doing construction on the Gowanus Expwy until December.I live on LI but im in Brooklyn often.

 

bajaman,

I replaced my stock rad (it was still working well, but this was for preventive maintenance purposes since it was 15 years old) with the one you recommended (brass OE replacement rad from radiator.com), and my FD now requires the cooling fans to come on more often to keep the temps down. I sealed along the sides of the rad, etc, so I don't think that's the problem. The temps now also seem to creep up on hard pulls when the ambient is above 80F. It never seemed to do that with the stock OE radiator.

So, my question is: since you recommended this radiator, how do you know it was better than the stock, OE, radiator?

 

I'm not defending bajaman, but there are a couple of questions that come to mind that might explain your experience OTHER than the radiator change...
What's your coolant/water ratio and is it the same as before the change?
Where are you getting temps?
Are you sure you comparing at roughly the same ambient (time of year)?
Any other changes in tuning or mods?

 

1. 50/50, same as before
2. Stock location, same as before (linearized stock gauge) - did not change the calibration
3. Yes - even at warmer temps with the stock rad, I did not see these temperature variations, and the fans (I have the Miata thermoswitch) came on only while sitting still.
4. None, although I did replace the WP with another stock (remanufactured) one from Malloy at the same time.

I'm even using the same type of gasoline - Sunoco 94-octane.

Add'l info - I lose no water, and the engine runs great otherwise. Other than noticing more temperature climb, and the fans coming on more often, there are no problems related to this.

My mods are in my signature.

 

Actually, I did do one mod at the same time - I put a restrictor in the water line off the bottom of the Pettit AST, the same size as the restriction in the stock AST.

EDIT:
My guess as to the cause of the temperature increases and increased cooling fan use:
The OE rad is denser (more closely-spaced fins) than the radiator.com brass rad, and thus requires less airflow to get the same amount of cooling (or conversly, with the same airflow, cools better). With the stock AC condensor and the stock hood in place, there may not be enough air-flow to make the radiator.com version work properly. The brass may conduct heat better, but the problem here appears to be not enough surface area to transfer sufficient heat to the air.

Therefore, I infer that going back to the denser stock rad, or a thicker aluminum aftermarket rad (Fluidyne?) would probably solve this.

Anyone else have any thoughts on this?

 

As I asked above, anyone else have any thoughts on this?

Also, since it's almost impossible to COMPLETELY seal around the radiator, etc, how much non-sealed area is likely to cause a problem? X square inches total unsealed, how big does "X" have to be to cause a loss of efficiency? Anyone have experience with this on an FD?

 

Your higher than old temperatures just make no sense. However, as I stated in my PM to you the other day, I changed....everything....in my engine from the old radiator to the new, as I replaced the radiator during my recent rebuild.
I have no 'real' data, i.e. accurate temp logging from an aftermarket ECU, other than I know how my car runs now, and it is much better, running much cooler than before. Old radiator (and admittedly old engine), the car would stall out sitting at stop lights, I would have to shut off the a/c to keep things from really overheating.
Fans were on ALL the time, it seemed. If I let the car idle in the drive the fans came on and stayed on. Now, the fans will cycle on for a couple of minutes and then shut down. No more stalling...at all. I run the a/c non-stop, even in heavy traffic and the RPMs don't fall off like before.

All I can say is I am sincerly sorry if you took my recommendation as gospel and are now seeing a situation not to your liking. There are a lot of us running the radiator.com all-metal OEM replacement radiator and having no problems.
Not to get into this a whole lot, but aluminum racing radiators are not INHERENTLY better. I hope you find a way to bring your temps down to a level you are happy with.

Good luck

 

bajaman,

Thanks for your concern and your PM.

I am certainly not placing any blame on anyone for the temperature increase I'm seeing. I just didn't expect this result. I'm just trying to get to the root cause of this before I do anything that costs more money (like getting a new stock or aftermarket rad like a Fluidyne), and maybe won't fix the problem.

Since this is not causing a huge problem, I think my next move, when I get the time, will be to pull everything (PFS IC duct, IC, air intake, etc.) off so I can make sure all the areas where air could sneak around the radiator are completely sealed. I think it is sealed as well as it was with the stock rad, but I will inspect it VERY closely this time to make sure.

 

The whole thread and no one answered the simple(?) question originally asked. . . what's the difference in these two radiators? (unless I missed it somewhere in the fine print)

 

The N-Flow is advertised as being 53mm thick, with a multi-pass design. I haven't been able to find much information on the Koyo "racing" radiator.

From the price difference, I'd bet the standard "Racing" radiator is a single-pass design, and not quite as thick.


-s-

 

anybody got diemensions on the fluidyne?

 

Fluidyne is a direct fit of the stock radiator just a bit more thicker. Great radiator!!

 

 

breast specialist ^

 

I have the Koyo racing radiator - it is also two inches thick. I think the "N Flow" is called that because the water flows through it like an "N" - first down half of the radiator, then back up and down through the second half. So yeah, it is a dual pass design.

My car now runs very cool, typically around 180 F (82 C). Under high load conditions, It gets up to 195 F (90.5 C). This is all without "N Flow". I did also upgrade to R1 dual oil cooler setup and downpipe. These are also helping it run cooler...

 

Don't have demensions, but about 50% larger than stock.
It's a good piece, but not necessarily a " direct fit".
https://www.rx7club.com/showthread.p...light=fluidyne

 

+1

 

Since you ^^^ and bajaman seem to know more than the rest of us, why don't you enlighten us?

My understanding is that given typical radiator (or inter-cooler) construction, the key parameter which controls how well it will cool is VOLUME. Volume is a combination of thickness, width, and height. Given oem fitment, the width and height are fixed. So thicker is more volume is more cooling, right?

 

Core volume is a factor, but not the limiting factor for most FD applications. The stock core has adequate capacity to reject heat for all but the most severe applications (I will grant you that the plastic end tanks are vulnerable to failure).

Heat rejection is limited by the amount of cooling air you can get through the radiator and is the big equalizer between the better radiators in this application. The biggest challenge is getting adequate airflow through any radiator you put in the FD.

 

As I just proved (at least to myself), you are ABSOLUTELY correct! Changing from the radiatorworld.com (CSF) copper/brass radiator back to the OE unit solved my temperature problems.

Heat transfer to air is inefficient at best, and is the limiting factor in almost any radiator application.

Dave

 

OK it is about airflow. However, given an oem installation, the airflow you get is the airflow you get. If your claim that the oem radiator "stock core has adequate capacity" were true, then it should not have made my car run cooler to install a Koyo radiator with twice the thickness.

On the other hand, I made all kinds of changes to make it run cooler, all part of a rebuild. So maybe the radiator made no difference! Nevertheless, just review back in this thread where I posted a photo of the Koyo side by side with the oem. The oem is a joke, period.

https://www.rx7club.com/showpost.php...7&postcount=19

 

There are a lot of factors that determine how well your cooling system works. I'm not claiming to be an expert, but here are a few things that I've learned:


The coolant passing over the hot metal parts is how heat is transferred. Assuming it's not boiling (which isn't always a safe assumption), water will transfer more heat than glycol (antifreeze). To prevent water from boiling, be sure the system is sufficiently pressurized, without any leaks. Adding antifreeze to the coolant will raise the boiling point, but it decreases the amount of heat transferred. Mazda has published recommendations in the owner's manual, they are a good starting point for choosing you water/antifreeze ratio.


After being heated by the engine, coolant gets pumped through the radiator, where it transfers heat to the radiator. Then, the radiator transfers that heat into the surrounding air. If the surrounding air is cool, more heat can be transferred from the radiator (and the coolant). If there is more air flowing through the radiator's fins, more heat can be transferred from the radiator.


A thicker radiator will hold more coolant, so it should be able to transfer more heat, assuming there is enough airflow. However, it will be more difficult to force air through the thicker radiator. I don't know exactly how much more difficult, and some people claim this isn't an issue.


Back to the issue of coolant flow, remember that our OEM thermostat is not fully open until 205F. This means that if your coolant temps are below 205F, not all of the coolant is travelling through the radiator. I think this is something that many people ignore. If your coolant temps never exceed 205F, then I would say your radiator is large enough. If you want coolant temps to always be below 200F, even during long periods of hard driving, you'd better look at drilling your thermostat or buying one that opens at lower temperatures.


Based on my experience, I'm going to assume that our OEM cooling systems are airflow limited. Cruising on the highway at 70mph, I have measured coolant temps decreasing (by about 5F) when activating the cooling fans. I noticed this both with and without a vented hood installed. This could also suggest that I need to improve my ducting and clean the fins on my radiator, which is pretty old.



To summarize, if you want an efficient cooling system, you need a lot of coolant and a lot of air flowing through your radiator. The radiator's volume is only part of the equation.



More info here, see tech tip #5:
http://www.stewartcomponents.com/Tech_Tips.htm


I've also compiled a lot of my cooling system research and posted it in this thread:
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/big-fat-fd3s-cooling-thread-571088/


-s-

 

That Koyo would be significantly heavier than the OEM radiator when full of water. Mazda's engineers were trying to make the FD lightweight, so I would bet that the OEM radiator works pretty well for a car that only makes 255hp.


Don't forget that the only upgrade to the powertrain of the R1 models was an additional oil cooler. Also realize that the airflow to the OEM oil coolers is very poor, and they don't have a fan to force air through them when they're hot. If you've got low-speed cooling issues, I would look to the oil system before the radiator.


-s-

 

Good info Scotty, thanks. As I mentioned, I made many changes to improve cooling, so it probably is not fair to attribute too much of my cooler running to the radiator itself. Probably putting too much stock in my improved radiator.

I also added the dual R1 cooler setup and I drilled two 3/16 inch holes in my thermostat. Maybe the latter is what really allows me to run cooler.

How do you activate/de-activate your fans to perform the highway airflow test?

 

Fluidyne is a direct fit. Jeff and Allen at Rotary Power just replaced the original radiator in my '93 because the plastic on the bottom was starting to crack and was brown in color. According to Jeff, there is more labor involved to fit a Koyo.