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Old 07-03-2015, 02:05 PM   #1
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Default Stupid fans question (butthurt is welcome)

I've run the 12" Ebay fans, but never in the summer heat with the A/C on, and with the custom shroud the system is overheating.

So, therein lies a stupid question. Which fans should I replace mine with?

All answers are welcome, from "Get the Spal 12" Extreme Performance, they're worth the money, *******!" to "Silicone Intakes 12" fans are pretty decent despite a measly cost", to "this ****** should be shot at sunrise for even asking about the dead horse"

Still, even though the cost of Spal is less than what I'm about to spend on rebuilding the engine, it's a little pricey ($190 per fan for the 12" Extreme that patsmx5 uses), plus I'm kinda all thumbs when it comes to fabbing alternator support and such.
It'd be nice to find a plug and play. Although if going the "make your own solution" is necessary, it's still a small cost to pay to ensure that the engine doesn't blow up.

Right now the stack is as follows; intercooler, P/S cooler (little tranny cooler), A/C condenser, custom rad (with a shroud).

Again, thank you all for taking the time to even read this drivel.
Peace!
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Old 07-03-2015, 02:32 PM   #2
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For a plug and play solution, FM sells a nice fan/shroud setup. They have 2 different fan options, go for the better fans.

For a non-plug and play solution, I would more or less copy the FM setup.

I wouldn't recommend the SPAL Extreme performance fans unless you absolutely have to have the best fans. They are the best, but it was a huge pain to get them working well. 2 different high output alternators, , custom bracket to mount it, air solenoid that opens to idle engine up when fans turn on high, series/parallel controller for 2 speed functionality without large inrush current, packaging them to not hit everything, finding relays beefy enough to not die, fuses big enough to not blow. Yeah... It wasn't plug n play.

Post pics of your heat exchanger setup and shrouding and ducting. Also what year miata.
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Old 07-03-2015, 02:35 PM   #3
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'91, I'll have to come up with the pics later.
Also, the FM is not an option due to the custom shroud around the custom rad.

(Btw, would a top shot suffice, or do you need a better (more detailed pic)?)

Thanks, Patrick!
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Old 07-03-2015, 02:39 PM   #4
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More pics the better. How is your ducting in the front end? Do you have the plastic undertray? Both of these are HUGE in keeping your miata cool.

If the FM option won't work then your best bet is to copy their setup. My testing on the ebay fans for a rear mount a/c condenser shows 3/4" thickness for the fan shroud was the minimum, less than 3/4" really hurt flow. I'd try to keep it 1" and then buy the best SPAL fan that will fit short of the extreme performance fans, unless you like building custom alternator brackets.
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Old 07-03-2015, 02:43 PM   #5
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I couldn't afford (due to the space constraints) any depth to the shroud. All it really does is seals the open areas around the fans, thus I'm looking to replace the Ebay junk ones.

I'd like to go with the Silicone intakes option, since they really look like what I have (btw, you can see my rad in the first post' link). It'd be nice to just bolt the suckers on and wire them up.
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Old 07-03-2015, 02:48 PM   #6
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If the car overheats below 25mph, you need better fans/shroud

If it overheats above 25, you need better ducting, or a better heat exchanger layout to get more unblocked airflow to the radiator.

I looked at the pics I didn't even see a shroud. Hmm. Can you move the radiator forward more to gain some clearance? Fans aren't going to do much without a shroud, especially slim fans.

Basically, I don't think it's possible to bolt a slim fans (any brand) to a thick radiator with a/c and intercooler and it not overheat on a hot day at low speeds. You need more airflow through the stack than you'll ever get with slim fans and no shroud.
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Old 07-03-2015, 03:05 PM   #7
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Car doesn't overheat, except when on a hot day, trying to run the A/C.
Apart from that, the cooling is sufficient (even without the reroute [interim engine, the turbo one is being rebuilt, thus no reroute on this one]).

With the turbo engine, with the reroute, without the intercooler, there were no heat issues whether on the track on a hot day, or sitting in traffic in scorching heat. No A/C, but the condenser was there [no shroud, the fans were bolted right to the rad].

Right now, the only time I boil the water is when it's above 90 out and I'm trying to run the A/C. I suspect without the reroute the engine isn't getting the proper flow and decent cooling, plus the fans are rather weak.

Perhaps Silicone intake ones (12") is the answer?
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Old 07-03-2015, 03:08 PM   #8
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Quote:
Originally Posted by alik View Post
Car doesn't overheat, except when on a hot day, trying to run the A/C.
Apart from that, the cooling is sufficient (even without the reroute [interim engine, the turbo one is being rebuilt, thus no reroute on this one]).

With the turbo engine, with the reroute, without the intercooler, there were no heat issues whether on the track on a hot day, or sitting in traffic in scorching heat. No A/C, but the condenser was there [no shroud, the fans were bolted right to the rad].

Right now, the only time I boil the water is when it's above 90 out and I'm trying to run the A/C. I suspect without the reroute the engine isn't getting the proper flow and decent cooling, plus the fans are rather weak.

Perhaps Silicone intake ones (12") is the answer?
What speeds does it overheat with a/c on a hot day? Idle? 20mph? 40? 60? 70?
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Old 07-03-2015, 03:09 PM   #9
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The AC condenser right in front of the radiator serves to artificially raise the ambient temperature, your radiator is getting pre-warmed warm air. It obviously doesn't do this with the the AC off.

More fans is the only answer, or go off the deep end like Pat and move the condenser.
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Old 07-03-2015, 03:11 PM   #10
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Or do more fans AND move the condenser.

But yeah, OP, I would seriously look to see if there's any way you can move that radiator forward some. That will give you more space for a shroud, or for better fans, or both. You need airflow.
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Old 07-03-2015, 03:13 PM   #11
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Also if you buy fans, buy SPAL fans. They are the best. So that would be a no for silicone intake fans if you're asking me. But I would do everything possible to give yourself more space before buying fans, as a medium profile fan will have a bigger motor/flow more than a low profile fan. You want the biggest you can fit to get more airflow.
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Old 07-03-2015, 03:14 PM   #12
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Quote:
Originally Posted by patsmx5 View Post
What speeds does it overheat with a/c on a hot day? Idle? 20mph? 40? 60? 70?
Idle not so much, but at any speed above that.
I've had it hit the "nuclear meltdown" (about 3/4 of the way, didn't wanna go any higher) at highway speeds and while puttering in traffic.

I suppose what Tommy has said is true. Too hot an air hitting the rad, thus raising the ambient, and fans aren't mighty enough to overcome that.

Gotcha, Patrick. Spend the money on Spal.

Curved blades? Straight? (it is my understanding that straight ones make the most noise, right?)
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Old 07-03-2015, 03:18 PM   #13
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Oh, yeah. Moving the rad, no.
The rad is beefy and low. It is flush against the front frame, and on the back there's the sway cutting off the room to play with.
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Old 07-03-2015, 03:20 PM   #14
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That sounds more like inproper shrouding, you don't need more fans if it doesn't overheat at idle.

You need to be aware of heatsoaking the radiator though, are you certain it's not getting hot while idling, using all the cool radiator water, then going hot just as you start moving, sucking the now hot radiator down?
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Old 07-03-2015, 03:21 PM   #15
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Curved are quieter and slightly more efficient, straight blades are louder and move a touch more air for a given motor. That's what I read anyways.

My Spal extreme performance fans have a curved blade, funny enough. But the pitch on them is comical compared to their regular fans.

I'll steal a few pics

Some SPAL fan, low profile:


Another SPAL fan, low or medium profile
[/QUOTE]


Extreme performance
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Old 07-03-2015, 03:30 PM   #16
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Tommy, I had the same rad and the same fans when tracking the car. The only difference is the addition of the intercooler and the shroud and lack of coolant reroute.

Coolant reroute would ensure that engine is cooling off universally, and not having the back cylinders run hotter than the front, correct?
Intercooler would rob some of the airflow, yes?
And, shrouding would only assist in having ALL the air flow through the fans, as opposed to having nearly half of it escape through the openings, so..

It'd seem to me (and I'm only a computer engineer, not a mechanical one) that the better flow (more air) would compensate for the hotter (no reroute, condenser heating up the ambient) air going through the rad, right?
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Old 07-03-2015, 03:40 PM   #17
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When you say shroud, what do you mean? Fan shroud, or radiator shroud/ducting? Are you using the factory undertray?

A fan shroud seperates the front and rear face of the fan, so that it is forced to pull air from in front of it instead of beside it. The more resistance (intercooler, evap, thick core) the more it's gonna matter.

Ducting forces the air through the radiator instead of letting it pass under while moving. You can go search up on how important that is if you'd like. After 20 miles an hour or so you should be able to cool better than thousands of dollars in fans...
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Old 07-03-2015, 03:41 PM   #18
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<p>
Quote:
Originally Posted by alik View Post
Tommy, I had the same rad and the same fans when tracking the car. The only difference is the addition of the intercooler and the shroud and lack of coolant reroute. Coolant reroute would ensure that engine is cooling off universally, and not having the back cylinders run hotter than the front, correct? Intercooler would rob some of the airflow, yes? And, shrouding would only assist in having ALL the air flow through the fans, as opposed to having nearly half of it escape through the openings, so.. It'd seem to me (and I'm only a computer engineer, not a mechanical one) that the better flow (more air) would compensate for the hotter (no reroute, condenser heating up the ambient) air going through the rad, right?
</p><p>&nbsp;</p><p>reroute also makes the system as a whole more efficient, its not just about making it equal.</p>
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Old 07-03-2015, 03:42 PM   #19
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Yes, I'm using factory undertray, and, rad shroud (to force all the air through the fans, as opposed to around them).
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Old 07-03-2015, 03:43 PM   #20
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Also, with the coolant temperature sensors being in the back of the head they'll read funky. I doubt they get much flow as the thermostat opens and closes, that's why we reroute.

It's still that hot back there though, it's not worth ******* around on. Reroute or die.
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