818S Radiator Fans -- Both?

[mistasherm]

Looking for some advice/assistance here. I am running a Mishimoto OEM radiator with both donor ('03 WRX) fans mounted. Do I need both fans since one was used for the A/C? If having both is a "nice to have," then can I wire them together (they both have identical four wire connectors)?
Thanks!

[wallace18]

I used both. even without A/C. But I am in FL and need all the cooling you can get.

[phil1734]

None.

They're only used when the car is idling for long periods of time, otherwise the air you're driving through provides way more cooling then any fan ever could. (The maximum wind speed off them is something like 8-10mph, so if you're moving faster than that they don't do anything and are actually an obstruction to flow.)

The last autocross I did was ~75F and sunny and my battery had died a few days before so I just left my car idling in between runs. Probably about 20 minutes of idling followed by 90 seconds of flat-out for an hour and a half. Not once did the temperature needle fluctuate. There's 15ft of additional aluminum tubing in there from stock, plus another 10ft of corrugated tubing, plus the radiator is tilted forward so heat can rise off it more efficiently. Trust me, if you have any sort of cooling issues on this car it's because you're making a ton of sustained horsepower (R-guys) or you haven't gotten all the air out of the system.

[SixStar]

With all the reports of overheating and engine failures directly related to coolant temps it would be foolish to not run both fans. What's the harm?

[mistasherm]

With all the reports of overheating and engine failures directly related to coolant temps it would be foolish to not run both fans. What's the harm?

I'm not concerned about weight - the car will not be tracked. I was going to run them via a manual switch as well, not sure if that is doable or if I should run them on separate switches.

[mikeb75]

My not OEM radiator has 2 fans. I left 1 controlled by the ECU, and run the other one by overriding the AC circuit with a switch.

[mistasherm]

My not OEM radiator has 2 fans. I left 1 controlled by the ECU, and run the other one by overriding the AC circuit with a switch.

Mike - that is the route I will more than likely take with these fans. I've got Wayne's mod on the crossover pipe so I should be set. I am leaning more toward reliability on this one.

Hope the gig in B'more is going well for you and that you've mastered that commute. I am going to give the key a turn for the first time here in the next couple of weeks...hopefully.
Ty

[Bob_n_Cincy]

I am running 1 fan.
The front Sirocco Radiator in the picture below is part of my Awic System.
The one behind it is the engine coolant radiator.
During a 1/2 hour track session the single fan doesn't come on until I make it back to the paddock area. Very repeatable.

I do have a fan override switch on the dash if I want to leave the fan on.

During street driving, It is the off on the highway. It town I world guess that it's on 25% on the time in stop and go commutes.

https://thefactoryfiveforum.com/attachment.php?attachmentid=85257&d=1519966330

[AZPete]

I can't help answer your fan question, but maybe you can help me sleep through the night . . .
The WRX has one fan with 5 blades and a second fan with 7 blades. Why the difference? I assume the Subaru engineers had a reason, but does anyone know what it is?

[Bob_n_Cincy]

I can't help answer your fan question, but maybe you can help me sleep through the night . . .
The WRX has one fan with 5 blades and a second fan with 7 blades. Why the difference? I assume the Subaru engineers had a reason, but does anyone know what it is?

I'll take a WAG at this question.
By having 2 different blade counts, you get 2 different audio frequencies. The result is quitter than if both were the same frequencies and the noise was additive.
Anybody else have a guess? Maybe somebody really knows the answer.
Bob

[mistasherm]

Pete - I noticed that as well, I'd be interested in the reasoning. I do like Bob's answer though, makes sense and a good argument.

Thanks for all your input. This forum has been wealth of knowledge as I have gone through my build (I am mostly a lurker) - and I hope to be turning the key for a first start in the next couple of weeks. First start is dependent on soccer games, hockey tryouts, golf clinics, honey-do lists, open houses (we are attempting a move), and random skyzone/roller rink/laser tag birthday parties --- so yeah, not much going on.

[turbomacncheese]

I've noticed that the fans labeled "quiet" often have more blades with less pitch. Interesting to consider interplay between frequencies of the two fans, but doesn't the AC fan ALWAYS come on after the main fan? It would make a little sense for that one to be a quiet fan, if one really cares about that sort of thing.

[Bob_n_Cincy]

I've noticed that the fans labeled "quiet" often have more blades with less pitch. Interesting to consider interplay between frequencies of the two fans, but doesn't the AC fan ALWAYS come on after the main fan? It would make a little sense for that one to be a quiet fan, if one really cares about that sort of thing.

IIRC both fans have unevenly spaced blades.
My OEM setup always runs booth fans.
Slow speed. Both fans in series (6 volt each)
High speed. 12v each fan.
Bob