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Old 09-23-2010, 10:44 PM   #1
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Thumbs up engine overheating cooling fan issues

hot weather here in saint louis, anyone know how to get both fans on at the same time without the a/c on. my car runs great in reasonable weather, the intercooler is obviously affecting the airflow temp through the radiator. temp climbs to almost overheating on 95 degree plus days and as soon as i turn on the a/c the second fan kicks in, temp comes down. i can do the same thing with the heater on, but darn it gets hot. I need both fans to run without the a/c on. Anyone can help i would appreciate it.
thanks
jim
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Old 09-23-2010, 11:00 PM   #2
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Option 1: http://www.miata.net/hakuna/parallel...%20wiring.html

The above may potentially blow the fan fuse and/or decrease the life of the fan relay. The "proper" way to do this mod would be to conjoin the control signals for the two relays, however on the 1.6 this is not easily done as the same relay drives both the A/C fan and the A/C clutch. Try option #1 first, and if that doesn't work, I'll draw you a picture of how to modify the harness to install an additional fan relay for the A/C fan.

-OR- just fix whatever is causing the overheating in the first place.
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Old 09-23-2010, 11:07 PM   #3
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Old 09-23-2010, 11:10 PM   #4
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Been running mine that way (Option 1) since I put the "A/C" fan in. My car was a base model never had A/C or P/S. So I got a fan off a junker and now have twice the fan power.
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Old 09-24-2010, 08:58 AM   #5
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Disconnect the compressor wire and push the A/C button.
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Old 09-24-2010, 11:05 AM   #6
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if you cant get temps down with the one fan, you need to revisits your cooling system.
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Old 09-24-2010, 11:08 AM   #7
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Quote:
Originally Posted by Braineack View Post
if you cant get temps down with the one fan, you need to revisits your cooling system.
Yes, agreed. As a side note. when you put the two fans on the same circuit without strengthening that circuit. I found that just wiring them together dropped the fan RPM enough that with the AC running, the car was getting too warm at idle.
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Old 09-24-2010, 11:28 AM   #8
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In therory that shouldn't occur. Wired in parallel they should draw the same voltage. The amp load will go up, but the circuit should supply that no problem give it doesn't go over the rating of the fuse. Which in this case it shouldn't.
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Old 09-24-2010, 01:28 PM   #9
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Quote:
Originally Posted by Sokool View Post
In therory that shouldn't occur. Wired in parallel they should draw the same voltage. The amp load will go up, but the circuit should supply that no problem give it doesn't go over the rating of the fuse. Which in this case it shouldn't.
IxR, my friend.

Everything has resistance. Wire, fuses, relay contacts, terminals, they are all resistors.

As current passes through a resistor, there is a voltage drop across the resistor. As current increases, the voltage drop increases. The formula for this is V = I x R (V = voltage drop in olts, I = current in amps, R = resistance in ohms). Any voltage which is "dropped" across the resistance is essentially lost, it is unable to power the load.

I have no idea what the actual numbers are, but let's say that one fan draws 10A, the supply voltage is 14v, and the resistance across the whole fan circuit (fuse, relay, wiring, interconnects) is 200 milliohms (two tenths of an ohm.) In the case of a single fan, 10 x .2 = 2, so from the original 14v supply, the fan is only seeing 12v.

Now, throw a second fan on the line. 20 x .2 = 4, which means that the fans are now seeing only 10v (14 - 4).

Annoyingly, this relationship isn't linear, either. That voltage which is being dropped is generating heat in the conductors and contacts. As the temperature of a conductor increases, so does its resistance. So more drop = more resistance = more drop = more resistance = more drop (...) until eventually a point of equilibrium is reached.

(This is how light bulbs work, incidentally. When cold, they draw many amps. After a few tens of millisecons, as the filament becomes very hot, its resistance shoots up and current drops to the "rated" level. Were it otherwise, light bulbs would simply explode.)

(It's also the basic operating principle behind hot-wire MAF sensors. The air passing over the wire cools it, resistance drops, current increases. Airflow increases, more cooling, less resistance, more current. Airflow drops, less cooling, more resistance, less current.)



Like I said, I'm just pulling these numbers out of the air- could be more, could be less. But that's essentially what's going on.
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Old 09-24-2010, 02:23 PM   #10
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Quote:
Originally Posted by olderguy View Post
Yes, agreed. As a side note. when you put the two fans on the same circuit without strengthening that circuit. I found that just wiring them together dropped the fan RPM enough that with the AC running, the car was getting too warm at idle.
I'm seeing the drop in rpm with the fans wired in parallel. I am also contemplating going away from the parallel fan setup. If at the track, I can just unhook the ac compressor and push in the AC button. Two fans seem like overkill on the street if the undertray is in place.

Joe,

would you post the wiring diagram you mentioned to correctly wire the fans together?
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Old 09-24-2010, 02:50 PM   #11
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Don't have a specific diagram. I didn't do it.

I Went back to the two fans set up as OEM and decided to pull the AC clutch connection off if I needed more. I didn't need more. Didn't overheat again.

Next time I go to the track I will disconnect the clutch wire and be ready if I need more cooling.
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Old 09-24-2010, 03:18 PM   #12
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Old 09-24-2010, 03:27 PM   #13
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Note that I made a change to the circuit in the link posted above. Be sure to refresh.
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Old 09-24-2010, 05:08 PM   #14
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Quote:
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Looks good! Thanks.
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Old 09-24-2010, 05:33 PM   #15
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Wouldn't it be easier to run a single wire and a diode to trigger the coil in the A/C relay? You could source switched power or ground from the man fan relay socket.

Edit: Nevermind, that would be dumb, it would turn on the compressor too.... Sorry
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Old 09-24-2010, 06:16 PM   #16
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Let me explain a bit more. Before the turbo, intercooler, the car would NEVER heat up at all. After the install, and only on hot days do I see the temp gauge rising up too much. Obviously the addition of the intercooler in the front of the radiator is causing either an airflow restriction or just enough heat passes out from it directly into the radiator and the one fan just can't keep up with the additional heat. I can't see any difference in timing or boost or anything to make me think otherwise. Thanks for the help
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Old 09-24-2010, 10:53 PM   #17
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your running the factory under tray, right?
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