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Koyo's New S2 Radiator (48mm)

Old 06-02-2015, 10:38 AM
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^I'll be interested to hear your results. Mine is ready to go in, but I'm still waiting to get my engine back.

I have datalogs with air intake and coolant temps I can compare when I next get on track, and I will post them here, but it won't quite be a direct comparison since the engine will be slightly different, and I will likely go with a higher % of water to coolant n the system.
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Old 06-02-2015, 11:19 AM
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I have extensive data logs as well. If I manage to see 5F cooler temps while on the track and somewhat faster recovery times, I will be a happy camper and consider it money well spent.

I bought 2 gallons of FL-22 off Amazon. Between old coolant left in the system and a little distilled water if needed, that should be enough. Since my car doesn't leave the garage when it is under 50 degrees, going a little light on the ethylene glycol should be more than fine.

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Old 06-02-2015, 01:28 PM
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Forgot to follow up. S2 radiator fits the S1 fine. Extended bottom mount pins do not require cutting. Could probably even re-use the S1 fan/shroud assembly, just that only one of the two top shroud mounting bolts will line up, should not be an issue IMO.
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Old 06-10-2015, 07:23 PM
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New radiator arrived today. This came from TH Motorsports and cost $302 delivered. Koyo does an excellent job of packing these things to prevent damage. I was appropriately impressed. It is not the best-crafted radiator I have seen, but it is a very nice piece, nevertheless. I will install it this weekend and track it on June 20. I collected good track data again yesterday for comparison. Ambient temp was 95F during the first 2 afternoon sessions, and peak coolant temp was 219F. Hopefully conditions will be similar in 2 weeks.















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Old 06-10-2015, 08:34 PM
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dang that looks thick. interested on how it fares compared to stock
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Old 06-10-2015, 10:52 PM
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Great looking Radiator there man.!
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Old 06-11-2015, 08:47 AM
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Just to echo something to keep in mind on your testing .... remember that the benefit of a larger radiator isn't really to reduce the temps on the track, but to _improve_ the rate at which the heat of the system is dissipated
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Old 06-11-2015, 04:01 PM
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Originally Posted by paimon.soror View Post
Just to echo something to keep in mind on your testing .... remember that the benefit of a larger radiator isn't really to reduce the temps on the track, but to _improve_ the rate at which the heat of the system is dissipated
why wouldn't a larger rad reduce temps ?
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Old 06-11-2015, 08:24 PM
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Originally Posted by paimon.soror View Post
Just to echo something to keep in mind on your testing .... remember that the benefit of a larger radiator isn't really to reduce the temps on the track, but to _improve_ the rate at which the heat of the system is dissipated
I'm afraid I must disagree. Once the thermostat is fully open, which means coolant flow is as unrestricted as it can be within the system, all that is left is the capacity of the radiator to reduce the temperature of the cooling vector. An all-aluminum radiator [better conductive potential], and one that sports a thicker core [greater cooling surface area and coolant volume], should increase that capacity over the stock configuration. That should result in cooler temperatures under maximum load.

You'll notice that I am not overly optimistic considering what I wrote above:

If I manage to see 5F cooler temps while on the track and somewhat faster recovery times, I will be a happy camper and consider it money well spent.
BTW, there is actually nothing actually wrong with my OEM radiator. There was a pinhole leak in the upper radiator hose that was stealthily snaking down--making it look like the lower tank was leaking. I replaced that hose and was fine to take the car to the track last Tuesday. Since I had already ordered the new radiator, I decided to just go with it. Hopefully I can install it tomorrow or Saturday.

Last edited by Steve Dallas; 06-11-2015 at 09:37 PM.
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Old 06-11-2015, 09:49 PM
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Originally Posted by Brettus View Post
why wouldn't a larger rad reduce temps ?
Originally Posted by stvnscott View Post
I'm afraid I must disagree. Once the thermostat is fully open, which means coolant flow is as unrestricted as it can be within the system, all that is left is the capacity of the radiator to reduce the temperature of the cooling vector. An all-aluminum radiator [better conductive potential], and one that sports a thicker core [greater cooling surface area and coolant volume], should increase that capacity over the stock configuration. That should result in cooler temperatures under maximum load..
I misspoke to a degree. I'm not saying it wont reduce the max load temp, but many times with aftermarket radiators, people _only_ look at the max operating temp as the end all be all of the radiators worth. The additional benefit of many aftermarket radiators is the delta T curve from the max operating temp to the idle temp.

I just mean if you see the temp just drop by lets say 3 degrees F, it doesn't meean the radiator sucks.
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Old 06-12-2015, 09:47 AM
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Just make sure you get that new radiator as well sealed as possible so that as much air as possible goes through it, not around it.

I was having some issues with heat (stock cooling system) even though I was running only in the fall and spring, so I did a bunch of work to maximize airflow through the coolers and it made quite a difference. I stuffed foam pipe insulation in the bigger gaps, used adhesive backed weather stripping and some aluminum ducting tape for smaller gaps and I zip tied the undertray to the AC condenser screen to keep it from deflecting away and letting air under the radiator. I also cut out the inner fender liners behind the oil coolers and riveted some mesh in there and I opened up as many of the blanked off grille pieces as was reasonable in an effort to increase airflow.

After doing that, I went from having to back off every few laps due to rising temperatures to being able to run flat out all session long in similar conditions.
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Old 06-12-2015, 03:30 PM
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I'd rather run the radiator fan continuously than seal off the radiator entirely to prevent air from backing up and creating a restrictive bow wave at the front of the car at track speeds. Some cool air getting to the engine bay is a good thing ...
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Old 06-13-2015, 08:09 AM
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I started the installation last night and stopped short of putting the new one in as I ponder foam strategy. The OEM radiator has heavy foam on the bottom and light foam along the top and edges. My thinking is that Mazda engineered more blocking at low speeds and less blocking at high speeds, and that fully sealing the radiator may not be the right approach. It seems some air is supposed to make it past the radiator and into the engine compartment as Team suggests.

Here is the OEM radiator with the foam attached:



Here is a comparison of the core sizes between OEM and Koyo:



I think a lot of people might not know there is a coolant drain plug on the left side of the engine block. If you back the plug out a few turns without completely removing it, about a gallon of coolant will dribble out in 30 minutes time. In the picture below, you can see it just to the right of the blue tape, which is there to cover a sensor harness and keep it dry.



Between draining the radiator and the engine block, you recover about 9.5 quarts, which means there is still roughly 1 quart in the system. That is close enough for me that I don't feel the need to flush the system the hard way.

More to come...
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Old 06-13-2015, 07:33 PM
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Originally Posted by stvnscott View Post
I started the installation last night and stopped short of putting the new one in as I ponder foam strategy. The OEM radiator has heavy foam on the bottom and light foam along the top and edges. My thinking is that Mazda engineered more blocking at low speeds and less blocking at high speeds, and that fully sealing the radiator may not be the right approach. It seems some air is supposed to make it past the radiator and into the engine compartment as Team suggests.

Here is the OEM radiator with the foam attached:



Here is a comparison of the core sizes between OEM and Koyo:



I think a lot of people might not know there is a coolant drain plug on the left side of the engine block. If you back the plug out a few turns without completely removing it, about a gallon of coolant will dribble out in 30 minutes time. In the picture below, you can see it just to the right of the blue tape, which is there to cover a sensor harness and keep it dry.



Between draining the radiator and the engine block, you recover about 9.5 quarts, which means there is still roughly 1 quart in the system. That is close enough for me that I don't feel the need to flush the system the hard way.

More to come...
Yeah did my first S2 coolant drain the other day (7 years old) and did not measure what I took out, only what I put in and got close to 10 litres (M Trans), 9.85 to be exact, inc coolant bottle, made certain HVAC was hot and hot tap left open.
AFAIK I think one has to disconnect battery cable or HVAC fuse within 60 seconds of Key off as the auto HVAC system auto shuts heater tap.

Unless one is tracking a lot in summer or in jams one can overcool too for 'normal' use.
And yes TEAM I have monitored (data logged) my coolant temps during our hot summers (normal car use) with IDS, and fan speeds would never cycle over to 3rd speed, usually 1, and 2 if with AC on.
Having said that there are huge differences between where I live and use my 8 compared to many in summer, getting stuck in traffic jams just does not happen with me and IMO is one of the (#1) RE engine killers for those who do in summer.
You can add huge radiators in capacity, which is all good, but how efficient is the water pump?, yeah I know another issue, when I recall the size of old 10 and 12A's WP's impellers, etc. , to the current WP's over the past 35 years used today are weeny.
RE structurally in design has not changed since 1969 10A, the barrel diameter is still the same, water galleries in housings are still basically identical.
OE Radiators, hose size and in and out was about 30% larger also back then.
My OE Radiator is fine for my use as my 8 is now a winter car only, NC is summer.

I sort of agree with TEAM as far as heat/air flow when car is idling for long periods in jams, but, when car is moving you need all the air going through the radiator...all a balance.
Mazda payed a lot of attention to air density pressures and flow through the car as Eric Meyer also said ''leave no gaps'', and on balance I have to agree.

I would set up a toggle switch on dash (for #3 Fan speed) to flick on if you get stuck at lights/jams to move air through constantly (all the time) rather than rely on Mazda's cycle on and off...tailor it to #2 speed if car runs too cold.
Which is what my friend Mark basically said, and I agree with this too.
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Old 06-13-2015, 07:44 PM
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And... Success!

The radiator is in. It is a very tight fit, but it does fit. The most difficult part is attaching the upper condenser mounts. There is zero room up there due to the thicker radiator core.

After pondering the foam a bit more and looking again at what Mazda did (and with fewer brewskis in me this time), I decided to go all the way with it. I glued it in place after installation with hi-temp RTV and held it with blue tape to dry.

Filling with new coolant was uneventful. It took 2 gallons of FL-22 and almost a gallon of distilled water, which is about a quart more than I removed. That ratio makes it roughly 40% coolant and 60% water if my back of the napkin math is right. That should be perfectly fine for my climate. I'll watch it for a few days to make sure it is actually full.















If you think you see a lot of damaged fins in these photos, let me 'splain. The upper radiator hose unexpectedly leaked some coolant as I was fishing the radiator in, and it collected in the fins of the condenser core. I washed it out with the garden hose, and what you are seeing is reflections of water.

Last edited by Steve Dallas; 06-14-2015 at 08:45 PM.
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Old 06-13-2015, 08:34 PM
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A couple more foam pics.




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Old 06-13-2015, 08:51 PM
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Originally Posted by ASH8 View Post
Yeah did my first S2 coolant drain the other day (7 years old) and did not measure what I took out, only what I put in and got close to 10 litres (M Trans), 9.85 to be exact, inc coolant bottle, made certain HVAC was hot and hot tap left open.
AFAIK I think one has to disconnect battery cable or HVAC fuse within 60 seconds of Key off as the auto HVAC system auto shuts heater tap.

Unless one is tracking a lot in summer or in jams one can overcool too for 'normal' use.
And yes TEAM I have monitored (data logged) my coolant temps during our hot summers (normal car use) with IDS, and fan speeds would never cycle over to 3rd speed, usually 1, and 2 if with AC on.
Having said that there are huge differences between where I live and use my 8 compared to many in summer, getting stuck in traffic jams just does not happen with me and IMO is one of the (#1) RE engine killers for those who do in summer.
You can add huge radiators in capacity, which is all good, but how efficient is the water pump?, yeah I know another issue, when I recall the size of old 10 and 12A's WP's impellers, etc. , to the current WP's over the past 35 years used today are weeny.
RE structurally in design has not changed since 1969 10A, the barrel diameter is still the same, water galleries in housings are still basically identical.
OE Radiators, hose size and in and out was about 30% larger also back then.
My OE Radiator is fine for my use as my 8 is now a winter car only, NC is summer.

I sort of agree with TEAM as far as heat/air flow when car is idling for long periods in jams, but, when car is moving you need all the air going through the radiator...all a balance.
Mazda payed a lot of attention to air density pressures and flow through the car as Eric Meyer also said ''leave no gaps'', and on balance I have to agree.

I would set up a toggle switch on dash (for #3 Fan speed) to flick on if you get stuck at lights/jams to move air through constantly (all the time) rather than rely on Mazda's cycle on and off...tailor it to #2 speed if car runs too cold.
Which is what my friend Mark basically said, and I agree with this too.
Thanks for the thoughtful insight, Ash. Being that I live in Texas, heat is a major concern. I do track my car in May, June, and September, in which ambient temps are usually in the 90s. Last Tuesday, it was 95 at the track, and next Saturday, it is expected to be the same, for example. I also have the joy of lots of stop and go traffic in my area. Another concern. Fortunately, my 8 is not my daily driver, so I can mostly avoid that, but it does happen occasionally.

I leave the 8 in the garage during the months of July and August. With temps over 100, it is too hard on both of us to contemplate taking it out.

Anyway, I replaced the radiator because I thought the original had a pinhole leak at one of the lower seams, but it turned out to be the forward upper radiator hose. I figured I could try this one and hope for slightly cooler running temps and somewhat faster recovery times. It is in there now, so we shall see...

I have kicked around that manual fan switch idea many times. It could happen.
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Old 06-14-2015, 08:31 PM
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A few more photos after completed installation with the undertray back on.


Left side foam.


Right side foam.


Bottom foam.


Top foam.



I took the car for a spin this afternoon to check things out after having performed the coolant fill procedure yesterday. I drove it from my house to Costco and back, which is about 6 miles each way. Once it was fully warmed up, I saw a 5.2F drop in cruising temp at 4K, from the usual 179.6F to 174.2F. When I arrived at Costco, I popped the hood and checked for any leakage, steam, or coolant level drop. I found none of those things. On the way home, I rowed through the gears a couple of times at high RPMs and pushed the coolant temp north of 195F, then went back to cruising at 4K. What used to take 5 to 6 miles in recovery only took about half that. The temp was back down to about 176F as I pulled into my driveway. Again, there were no signs of leakage, steam, or coolant level drop.

I am pleased with what I am seeing so far. There is definitely potential for a drop in overall operating temps without going too low. There is also potential for faster recovery times. I'll drive the car to work a couple of times this week and keep an eye on things. The real test will come this Saturday at the track, where I'll flog it hard for 150+ miles. I'll post before and after logs for comparison after that.

So far, so good!

Last edited by Steve Dallas; 06-14-2015 at 08:57 PM.
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Old 06-15-2015, 08:18 AM
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I woke up at 2:00 this morning thinking that running cooler at cruising temps makes no sense, as the thermostat is not fully open and should therefore be regulating the coolant temp to about the same temp as before. Maybe within 5 degrees is normal for mechanical regulation? Anyway, I paid very close attention to it on the drive in to work this morning, which is about 25 miles. I noted the following:

1. Cruising temp was mostly 179.6F as before
2. The temp would drop to the 174F range after rowing through the gears, but would climb back to 179.6 and stay there
3. Recovery was incredibly fast with an ambient temp of 76F

So, what appears to explain yesterday is number 2 plus stop lights that were spaced in such a way to keep me from seeing the cruising temp stabilize at 179.6F.

Things appear to be working as expected. Cruising temps are basically the same as before. Idle temps seem similar to before, but I don't have hard data for comparison. Recovery time after rowing through the gears is faster.

The $64,000 question is whether peak temps under high load will be any lower. I'll find out Saturday.

Last edited by Steve Dallas; 06-15-2015 at 09:03 PM.
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Old 06-15-2015, 03:11 PM
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Originally Posted by stvnscott View Post

Bottom foam.


!
I found I needed to physically hold the bottom foam in place or it just gets blown up and out of the way ..................
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Old 06-15-2015, 03:25 PM
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All of the theory is funny because we do so much to control things and then I know guys who track/autox without under trays, with stock radiators, no foam, etc. with no issues,
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Old 06-15-2015, 03:43 PM
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Originally Posted by 9krpmrx8 View Post
All of the theory is funny because we do so much to control things and then I know guys who track/autox without under trays, with stock radiators, no foam, etc. with no issues,
They probably don't have temp gauges either so they wouldn't even know if they were sitting at 230F ................
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Old 06-15-2015, 03:57 PM
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Nah, most do, including two turbo guys with no undertrays and stock radiators.
It drives me nuts but some people just get lucky I guess, I see cars all the time that are poorly maintained and have never broken down.
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Old 06-15-2015, 03:57 PM
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I have logged half a dozen rx8s at the track , most of them purpose built race cars . All of them have been running at around 105C and none of the owners thought there was any problem .
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Old 06-15-2015, 04:09 PM
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Well according to the FSM, up to 243F is safe
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