Why control dual cooling fans seperately?

[HOSTILETAKEOVER]

I bought a cool kit from Frank at Prodigy. It is made up of a radiator with two electric fans mounted on a fan shroud and a dual relay kit. The kit comes with a couple different wiring options for the relays.

What are the advantages of turning fans on and off individualy over turning both fans on when the coolant temp gets up or the AC is on?

[The WidowMaker]

the sound these things create and the amp draw is incredible so running both when not necessary is a waste. i havent set mine up quite yet, but my thoughts are that if set up for two, youll get two at idle, one at low speed and hopefully nothing at speed.

[Rhino]

Usually the fans are programmed to come on in a staggered approach. Let's say one kicks on at 180, and the second at 210. This allows you to use a single quieter fan the majority of the time, however also holds come CFM in reserve in case you ever get to the point of really needing it.

The second fan is also frequently used to help with air flow across the A/C condenser to help improve performance in stop and go traffic.

[H2Ogbodies]

precisely why single two speed fans are far superior. Usually space is tight so dual fans get the nod, but they are not the best at moving a lot of air with low amp draw like a single fan can. Most dual fans have pancake sized motors which are cheap to build but require a lot of power to run to move any decent amount of air-combine that with a slightly aggressive blade design and you have some loud fans. I put twin Spal fans in a V8 S-10 only because I could not fit a Mark VIII or any other Motorcraft fan in it and holy crap-those fans sound awful-way too loud. There are other two speed Motorcraft fans to use beside the Mark VIII and on low speed it keeps most engines cool and they are far quieter during operation.Like most things, it's a tradeoff of sorts.

[CreepinDeth]

Usually the fans are programmed to come on in a staggered approach. Let's say one kicks on at 180, and the second at 210. This allows you to use a single quieter fan the majority of the time, however also holds come CFM in reserve in case you ever get to the point of really needing it.

The second fan is also frequently used to help with air flow across the A/C condenser to help improve performance in stop and go traffic.

Exactly.

Plus if you stagger the low speed first, you don't have such a huge spike in amp draw to load the higher speed first.
Take the Taurus fan for example. It spikes over 100amps on startup if you skip the low speed setting.
Low = 2500cfm , high = 4500cfm
http://www.youtube.com/watch?v=gWJFzAMsIlc

However, I have mine on a 30amp breaker and it works just fine for both low and high speed.
If I just hooked up the high, I'd be tripping that breaker and the fan would never run.

[ProdigyCustoms]

Also remeber, if the A/C is on, a fan HAS to be on or high side presures will go through the roof quickly.

Hostile, you are familar with my Street Racer. Block filled to the bottom of the freeze plugs Small block 400 (famous water heaters even not filled), with our Prodigy Cool Package with dual 13" fans I cruise 125 miles Sunday and never had the second fan kick on (I was not ruunning the A/C).

[EFI69Cam]

Frank,

Can the spal fans on your radiator be wired in a series/parallel arangement like stock LS1 fans for high and low speed? If not is there any difference as to which one (driver or pass side) is fan 1?



Thanks

[ErikLS2]

Frank,

Can the spal fans on your radiator be wired in a series/parallel arangement like stock LS1 fans for high and low speed? If not is there any difference as to which one (driver or pass side) is fan 1?

Thanks

This would be the best way to do it. You'll just need a third relay.

[ProdigyCustoms]

No real difference as the condensor should be centered anyway. My my Street Racer there is a 1 and 2 because I have the transmission cooler in front of one fan and oil cooler in front of the other. Trans is more important then oil most times.

As for high and low? They can be run with a fan controller to variable the speed, high and low would be fine if the computer can send the proper voltage.

[H2Ogbodies]

Spal's controllers are designed to use there fans or lower rated fans-that would be the easiest thing to do. high speed and low speed settings need to be at least 15 degrees apart and i suggest running the controller off a relay that you can "drop-out" should you need a manual over-ride. Dropping out the IGN signal for example will not reset the controller. you dont want to power an over-ride while leaving the controller "live" should you opt for that method.

[J. Fast]

Thought I'd share some of my experiences with Flexalites, Spal, and now Derale. I ran Flexalites, boy those were terrible! I have a twin turbo setup car and everytime I drove up to the top of Eisenhower tunnel in Colorado (12000ft) I nearly had a heart attack watching my coolant temp push 240. I swapped those gems for some Spals and they worked pretty good. They actually held up to the beating and kept the temps under 210 but had problems when I stomped on it repeatedly. I have a buddy who made a reccommendation on a Derale setup. My first comment to him was Derale's are power suckers and the wiring is as elaborate as a traffic signal. I gave some 16925's a spin and came to find they're really darn quiet and move craptons of air those two little 12"rs moved 4300CFM combined. So far so good... no problems (x-fingers-x). In my opinion they make a really great high displacement radiator fan and they're quiet too! I just used one of their pre-configured relay setups ran a dedicated 30A and am quite happy .

Here's a link with some general info if you fellas are interested. http://www.derale.com/basic/default.aspx

J.

[Scarelane]

My builder tried putting one large fan in the center of the radiator, but there wasn't enough clearance. Had to go with a dual staggered fan set up. He was saying that the single fan did pull more cfm than the dual set up. We'll see how it works next Summer!!

[H2Ogbodies]

When you look at the thermodynamics of a radiator, using a large, single fan is far more efficient as it pulls air through the entire shrouded area instead of one area of it....so on low speed a single fan will move as much air as two smaller fans running at a higher speed. But space can be a determining factor when deciding on fans. I do like that DeRale is made in the USA-Spal is made in Italy and Flex-a-lite..well, idk...China I'd bet judging from their quality control craftmanship...lol.

[aronhk_md]

A single fan of proper design should always be more efficient than twins of half the size each. The same principles are involved that make a single boat prop more efficient than half sized twins, and similarly with aircraft large single props as opposed to smaller twins. I wont go into the physics of it, but you can look it up. As a matter of fact the same thing applies to a properly sized/pitched single turbo vs twins......the single SHOULD be more efficient (yes, its a common - and somewhat mistaken in my opinion -thought that twins will spool faster)

They are all air (or water) flow over a pitched and often complex "wing" (or multiple wings). Generally speaking the less BLADES (wings attached to central hub) the more efficient it CAN BE (Although here diameter has to be adjusted upward or blade surface area adjusted upward as the number of blades decreases to compensate.).

This is why the props on some of our most technologically advanced submarines are actually a single blade shaped like a corkscrew.

[J. Fast]

Another question I've always pondered and maybe someone can chime in. Is there an added benefit to puller fan over pusher fan? If they move the same cfm is one more efficient than the other?

[aronhk_md]

Another question I've always pondered and maybe someone can chime in. Is there an added benefit to puller fan over pusher fan? If they move the same cfm is one more efficient than the other?

I think that very much depends on the blade design......and really the only way to tell unless you did the designing yourself is to try it each way and to figure it out. I think it will vary with each fan. Most of the fans I have seen have been designed to pull....but that doesnt mean they wouldnt work well pushing. Either way having it all well shrouded will be important so that you are ONLY pushing/pulling through the cooling fins.

But there should be no COOLING benefit for one over the other if they move identicle units of air through the radiator.

[J. Fast]

Tieing this back to the original post would the most ideal setup be to put one large pusher and puller on and just use the second as a failsafe then and go with some sort of limit switch or temp switch for any situation which results in a coolant temp above say 200*F?

[H2Ogbodies]

Well a pusher by design will block some of the airflow through the radiator-making it turbulent. And, it's far easier to use the inside radiator area to keep it all shrouded vs. the outside what with the hood latch hardware, AC condensor, etc. getting in the way. If you have a good puller fan, pushers are not worth the extra hassle imo. I vote for a single large fan (where space permits) vs. ANY dual fan setup....ideally a two speed to keep it versatile.

[JRouche]

Well, I have a different problem. My engine is running too cold. I have a 180* T-stat in place. And its operational. The engine will get up to 180* when idling at a stop light on a warm day. But as soon as Im in motion the temps drop to 165*, way too cold. And Im getting good temp readings, I have two sensors, one for the gauge and one for the EFI computer. And they both show the same temp, its 165* while moving. Not cool.

I need a lil more temp for the engine. I have the sensor for the fan set at its highest limit (supposed to be 210 or so), and the fan doesn't run much at all, if at all while driving, just during a long traffic light, then it will kick on (prolly when the Stat opens up). And it settles into about 180* (the H2O temp), never higher.

I dont want to change the Stat to a higher number because it controls the flow just fine when Im at a stop and the heat builds up.

Its just during any driving, the temps are too low.

I have a large Griffin aluminum radiator, but I wouldnt think that would cool the engine down that much. I have the trans cooler right in front of it. I dont have A/C but might in the future. Maybe having that cooler in front of the radiator will help.

But for right now its too cold and running rich to compensate. I have advanced the spark timing as much as I feel comfortable with, leaned it out as far as I should go. Did all the things to bring the engine temps up, still running way too cool.

My engine should be actually running around 190* to get the best out of it. I hate the thought of changing the Stat cause it will over heat at a stop, or the fan will be working overtime to keep it cool. The engine isnt a slacker, it is 10.5:1 compression and running on the edge. The stat is fine, I think??, still go hotter?.

ERRR!!! Just one of those issues. Almost want to go out and buy an A/C unit too have the condenser up front to limit the air flow and heat the engine up some. Im not happy with the 165* temps right now, way too cold for an engine, specially an EFI engine.. Im wasting fuel and loosing power. Its running rich due to the temps givin to the computer. But more importantly its rich due to a cold engine. If the engine was around 185-190 it would be happy. Its cold and slow though. Id really like to see 190-195 on the temps. Sounds warm but with EFI thats a decent temp.

But I cant remove anymore fuel and cant advance the spark anymore than it is. Im almost to the point of blocking off the radiator to warm her up some. And NO, LOL, its not a diesel.

Any advice?? I need to warm the engine up some. I dont mind a lil more fan work on the stops with a warmer Stat if thats what it takes.

Kinda silly huh, looking for more heat. But thats my reality for now. Gotta get outta the 165* range. JR

[kryptik]

JR I am experiencing the same issue as you: 1970 Camaro RS with a GM zz383 properly timed, carbed. Running a large Alumitech radiator and Lincoln Mark VIII fan, 180 Robert-Shaw stat, manual trans.

Driving around town at low speed the engine will be perfect around 185-190, but when I go for a long cruise on the freeway (especially in 5th gear) the engine will be down around 165-170 which is way too cool; you can definitely notice poor fuel atomization occurring. The engine wont tug as hard, especially in 5th gear.

I am NOT running a vacuum advance (following 2010 GMPP zz383 documentation) which should have resulted in increased cruise temps, but they are still rock bottom. I even changed the thermostat from one with bypass holes to one WITHOUT bypass holes: the same issue remains just not as extreme (165-170 vs 140-150).

I THINK part of my issue is having a cowl induction hood which is not sealed to the air intake causing extreme airflow through the radiator and out the cowl scoop at 75mph. Since the cowl scoop is above the engine (obviously), all heat rises out. If it was sealed I have a feeling that engine heat would remain trapped under the hood, resulting in more stable temps.

Also possibly running a higher concentration of antifreeze in the coolant (I'm at 30% AF and 70% H2O right now) will reduce its thermal efficiency and get the temps where they should be.

Any ideas and/or insight would be greatly appreciated.
Matt