Moparts Tech Archive

Motor General

Fan Questions

Electric vs Clutch fan vs Solid fan

1980RR
New Member
Posts: 93
From: Palmer, MA
Registered: Oct 2001
posted 07-03-2002 11:50 AM

Right now I have a steel fan setup solid. I'm told that there is 15 horse in a clutch setup($90).
Questions:
1. Can I mount a clutch to my fan(jegs $30)
2. Will I gain even more horse going to electric
3. If so, I have one 10-12 inch fan. Do I need another.
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Tim Moffett
Moparts Member
Posts: 1302
From: Rochester, NY
Registered: May 2000
posted 07-03-2002 12:03 PM

From my experience, the difference between a clutch and direct drive fan is noticeable.

From what I have heard, clutch vs electric is not.
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jfsram
Moparts Member
Posts: 657
From: Hamilton, Ontario, Canada
Registered: Jul 2001
posted 07-03-2002 12:08 PM

The more rpm your motor sees the more beneficial a clutch or electric fan will have.
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Mike P
Moparts Member
Posts: 910
From: Stillwater, ny, usa
Registered: Aug 2001
posted 07-03-2002 12:18 PM

IMHO, Electric is the way to go, but I "feel" a difference with a Flex fan.
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1980RR
New Member
Posts: 93
From: Palmer, MA
Registered: Oct 2001
posted 07-03-2002 12:32 PM

Do you think one 12 inch fan will be enough? Do they work better pushing or pulling? The motor never heats up even in 100* temps. I don't want to create any problems.
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-03-2002 12:50 PM

I am very happy with my clutch fan. I tried electric and got tired of the wiring problems. The electric fans reduce the load on the waterpump and add to the load on the alernator so not much real gain there. Also note that the clutch fans release above a certain rpm when they are not needed anyway.
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-03-2002 12:57 PM

I could never get good, consistent cooling with the electrics on the TT340. Have been very happy since the switch to clutch.
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RangerDan440
Moparts Member
Posts: 184
From: Texas
Registered: Mar 2002
posted 07-03-2002 02:53 PM

RR-
I tried twin Tornado electrics for my 440, and like someone else said, they don't cool consistently. I go from as high as 220 in traffic to 170 on the interstate. I have them set up as puller fans inside the radiator for now, but I'm planning to reverse them to pushers on the outside and install a clutch fan for added air pull at idle. The electrics, perhaps because of their size, don't pull enough at low engine speeds where an engine driven clutch fan can. Maybe that's why trucks all come with engine-driven fans. On a mild, street driven car, the power loss is pretty negligible compared to the cooling advantages. At least it is in my case, anyway. Someone also mentioned alternator load-since installing the electrics, I'm not getting a full charge on my battery anymore. I'm gonna have to get a more powerful alternator. My .02.
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mayhem1974
Moparts Member
Posts: 278
From: chesapeake,va,united states
Registered: Apr 2002
posted 07-03-2002 03:14 PM

On the street I want a clutch fan.
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karfixer
Moparts Member
Posts: 994
From: Simi Valley, The People's Republic of California
Registered: Feb 2001
posted 07-03-2002 03:21 PM

I changed the direct 7 blade on my Barracuda to a 16" electric-this is a stock 318-2v- and it made an incredible difference Lost that heavy fan and it revs way better. Cooling is still about the same, but I will probably fab up a shroud to help with the summer heat.
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DONTDODGEITRAMIT
New Member
Posts: 66
From: Atlanta, GA
Registered: Nov 2001
posted 07-03-2002 03:52 PM

Well can't make any comments on the elect side of the house really. But serving in the military and logging many hours on hummers. They use a hyd set will act valve mounted on fender support and control by temp switch. When the puppy kicks in on the interstate you can feel it and hear it. Automatic loss of 10 mph and back up to speed when it kicks out. Makes passing a semi a real pain in the butt. So I guess the 64,000 dollar question which robs hp and mileage. Fan kicking in here and there or the alt taxing the motor to make up for the power drain? Due to the fact most cars now days use elect I would side on the elect side myself. Theirs my two cents.
But, clutch best all around, easy on the HP and no elect nightmares. Makes getting home without alt charging. Flex humm can't fig were I would use it maybe in a tight spot. Rad space.
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jodart73
Moparts Member
Posts: 836
From: Milton,WI, Rock
Registered: Jun 2001
posted 07-03-2002 04:38 PM

I have a 16" eletric on a 16X26" aluminum radiator on my warmed over 318, gets to 210 degrees in town, cools to 190 on the open road. I'm not that comfortable with 210 in town. Had a flex fan on there and never got above 185, but it was noisy and robs HP, will try a clutch fan this weekend and see how that works.
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-03-2002 04:40 PM

karfixer - You would have probably noticed similar gains going from a solid fan to the clutch fan.
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HemiDoug
Moparts Member
Posts: 365
From: Bowling Green, KY, USA
Registered: Apr 2001
posted 07-03-2002 05:25 PM

No one seems to have addressed 1980RR's question no. 1. You cannot put a direct drive fan on a fan clutch. The clutch fan has a large hole in the center to fit over the clutch hub. Both a clutch fan and electric fan will use less HP than a direct drive fan. The only reason electric fans are popular on stock cars today is the fact that the engines are turned sideways for FWD. Look how they cool trucks and rear wheel drive cars.
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Don1
Moparts Member
Posts: 3339
From: Valley City, ND. USA
Registered: Oct 2001
posted 07-03-2002 07:57 PM

Most electric fans will not efficiantly cool a V8 let a lone a warmed up one. For drag racing where the fan can run and cool after shut down is the big advatage to me. I can tell by engine RPM drop when my electric kicks in (thermostatic controled). The RPM's drop because of added electrical load.
Street driven I recommend a clutch fan.
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grinningdog
Moparts Member
Posts: 1415
From:
Registered: Nov 1999
posted 07-03-2002 08:08 PM

If you are not concered about the HP loss would not a solid fan give the best cooling?
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ChallengeMe
New Member
Posts: 3
From: Mission Viejo, CA
Registered: Jul 2002
posted 07-03-2002 08:17 PM

One point that has not been mentioned yet is that when the car is running at speed, the airflow through the radiator can keep most cars cool without a fan at all. So if you are using a thermostatically controlled electric, you will not have the alternator drag either, SOMETIMES. That does not mean I think the electrics are better, it's just one more fact to complicate the decision.
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Runner
Moparts Member
Posts: 2687
From: Lewiston, idaho
Registered: Nov 1999
posted 07-03-2002 08:34 PM

i have no problem with my 16" permacool fan and my aluminum radiator. ive always wonder how much power a clutch type fan robs when the engine does get hot and its locked up. the nice thing about electric is you can wire it to co0mer on automatically or shut it off or turn it on all the time, this has helped make my pig more consistant. i also like the factthat im almost always between 180-185 when im staged. the electric fan helps me control that also
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71scamp
Moparts Member
Posts: 1267
From: Akron, Ohio
Registered: Apr 2001
posted 07-03-2002 08:44 PM

I have track tested an electric vs. a flex fan and they ran almost identical. The flex fan is a few hundredths quicker due to the better cooling. The electric fan didn't do the job on the street. I haven't tried a clutch fan the past few years but I don't remember slowing down at all when I went from a clutch fan to a flex fan years ago.
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jodart73
Moparts Member
Posts: 836
From: Milton,WI, Rock
Registered: Jun 2001
posted 07-07-2002 01:34 PM

Sorry it took so long, but I tried to put the clutch fan on, and it was only about 1/8 inch from my radiator, too close for my comfort. Flex fan is back on, does a good job, and I guess I can live with the noise.
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-07-2002 02:50 PM

You need a clutch with a shorter shank. There are different lenght available
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craig440cuda
Moparts Member
Posts: 365
From: hopkinsville ,Ky
Registered: Mar 2002
posted 07-07-2002 04:02 PM

I switched from a clutch fan to an electric,gained .200 in the 1/8th mile.!!!thats 2 tenths!!!thats alot.like 15-20 HP.I have no cooling issues(stock radiator,318,16" electric fan)on my 69 dart.Also have one on my 440 Barracuda racecar,really helps cool radiatorFAST between rounds.I dont know about the extra drag on the altrnator,my car picked up bigtime .
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feets
Moparts Member
Posts: 3403
From: Irving, TX, USA
Registered: Jun 2000
posted 07-07-2002 10:22 PM

let me address something here...
I was running a Spal electric as a puller and had a generic 12" pusher for extra cooling at idle or when wrenching on the car.
When I drove the car with the auxiliary fan on, it would run hotter above 45 mph.
What it boils down to is that the air was moving across the fan faster than the fan was turning. Since there was an active electrical current, it essentially turned the fan into a generator. That actually blocked air flow.
Turning off the current flow to (from) the fan allowed the blades to spin freely. The fan would simply pinwheel to match the speed of the oncoming air.
Turning off the front mounted auxiliary fan at highway speeds would drop the temperature 8-10 degrees.
As soon as I get the room behind the radiator, the clutch fan is going back on.

If you're looking for a short fan on the cheap, so with a new non-thermal clutch and grab a fan blade off a van or large A/C equipped 70's C body. They usually have 5 bladed fans.
I've still got the 7 blade fan from my '74 Road Runner and it'll be headed for the hot rod ASAP.
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ianward
New Member
Posts: 61
From: Westbank, BC, Canada
Registered: May 2002
posted 07-07-2002 11:00 PM

I have a Flex-a-lite 260 which is two 14" fans that flow a whopping 5,000CFM when both on.
I wired an extra thermostat to one fan so now one fan comes on at 200 and the next at 220 deg.
Sitting in traffic with the A/C on at 100deg both fans actually reduce the temp qwik.

74 Charger Rallye MP 360/380 Crate stroked to 406”, Hughes stage 2 heads, 518 tranny+2800 stall, 83/4 4.10, All ram truck acc’s+Serpentine, Air, PW, PB, PT, Jacobs, Speed Demon 750.
Ian Ward
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Tim Moffett
Moparts Member
Posts: 1302
From: Rochester, NY
Registered: May 2000
posted 07-08-2002 08:07 AM

I lost about 1.5MPH by going to a flex-a-lite fan. Now, I am back to a clutch fan. Much better!
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panic
Moparts Member
Posts: 1198
From: Long Island, New York
Registered: Nov 1999
posted 07-08-2002 09:53 AM

Re: comment about fan kicking in on interstate - air volume through the core should be sufficient at any speed over 30. If you have your fan on above that speed, it doesn't work. Racer Walsh used to drive his Mustang on the street with NO FAN - only a problem in traffic.
Most electric fans simply aren't big enough - they're sold because they sound like a good idea.
IMHO - full-size steel fan blade with electric clutch like AC, switches out on:
> low vacuum for racing
> 2-3 shift or speedo signal
switches in on:
> brake light switch signal
> high temp
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-08-2002 10:07 AM

One other issue worth mentioning with electric fans has to do with mixtures and tuning. With a clutch or solid fan, you have constant airflow through the engine compartment, and because of the airflow, relatively consistent under hood temps. With electrics that don't come on until you are getting hot, the engine compartment temp can raise dramatically while idling. This heats up everything in the air and fuel system enough to make significant changes to the mixtures. It is particularly hard to tune, because when you first slow down, the engine compartment is cool, but then heats up, so you don't know where to make your settings. On the TT340 Challenger, I saw over 40 degrees F temp drop in the engine compartment by going to a clutch fan, from the electrics I used to run.
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88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 11:14 AM

Does anyone have CFM numbers on a clutch style factory stock fan. Cause if the Electric can flow big numbers then I would have to think that a properly installed electric (i.e. an electric with a fan shroud) would be better than a parasitic clutch fan. I was looking at the Flex-Lite 210 a couple of days ago for my truck. They claim a 2500cfm flow rate which seems like a pretty good number to me. Especially since the kit includes a shroud. I can see how if someone just went out and purchased a 12 incher and stuck it on their radiator without a shroud that it might not cool as well as possible??
Oh and it might be good to mention that I have a 95 C&^%y Impala SS which is rear wheel drive and also has dual electric fans. I would imagine that there was a reason why they did this.... But then again it is a C&^%y
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grinningdog
Moparts Member
Posts: 1415
From:
Registered: Nov 1999
posted 07-08-2002 11:37 AM

I still have my question. Would not a solid non clutch fan provide the best cooling if you are not worried about the HP?
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-08-2002 11:51 AM

Grinningdog: In my opinion, yes, without doubt.
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88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 11:54 AM

yes it would....
But who doesn't care about HP?
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grinningdog
Moparts Member
Posts: 1415
From:
Registered: Nov 1999
posted 07-08-2002 02:05 PM

Me I guess. If your not going to the track 300 + horsepower is more than you need or can use. 15-20 hp will not make any difference to me.
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-09-2002 12:32 AM

One of the mags (I think it was Car Craft) ran dyno tests on different fans. I'm gonna have to see if I can find it. The clutch fans did pretty good if I remember right.
Found it - it is the Car Craft May 2000 issue. It shows the elecrics and the clutch fans by far the best with the electric a little better. But for all the hassle of the electrics, I choose the clutch type.
The article in Car Craft didn't say how well they cooled. It was a horsepower test only.
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Electric fan worth the $$

88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 03:00 PM

OK so for the past few days there has been a side tracked post where a few people have stated their thoughts regarding electric fans. I have an 1988 D150 with TBI. I want a fairly stout running motor. Originally I wanted 300hp so I wouldn't suffer from withdrawal after selling my SS. But after some research I found that there were not that many parts that I could purchase for the 88 TBI. And I have to keep it TBI for now since I need to pass the sniffer test. So my question is are Electric fans worth any hp? And if so how much? I am looking at flex-a-lite 210 which is 2 12" fans pulling 2500CFM so I cannot imagine having a problem with overheating. But I am not sure that they will be worth the 200$ they go for...
What do the experts say?

Marcus
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Jerry
Moparts Member
Posts: 1145
From: WARREN, MI
Registered: Nov 1999
posted 07-08-2002 03:04 PM

electric fans are worth about 15hp. of course on a higher revving engine theya re worth more than on a lower revving one. assuming fixed fan. eventually those go into afan stall which is bad. i don't think that $200 is worth 15hp.
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rvoyles
Moparts Member
Posts: 1528
From: Bakersfield, CA.
Registered: Aug 2000
posted 07-08-2002 03:04 PM

"flex-a-lite 210 which is 2 12" fans pulling 2500CFM".....is that 2500 cfm per fan or combined? If its 2500cfm total, then thats not really very much and you could have cooling problems. if it's 5000cfm total then they should cool you fine....
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88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 03:14 PM

It is total.... So I would have cooling problems? It is a fairly stock 318(bigger cam).
Do you have any idea how much a fixed fan or a clutch style fan flows? Just curious what the difference might be...

Marcus
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-08-2002 03:16 PM
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Jerry
Moparts Member
Posts: 1145
From: WARREN, MI
Registered: Nov 1999
posted 07-08-2002 03:19 PM

i runa pair that has about 2500 cfm total and have no problems. i was running these with a built 360 with a two row 26*19 rad. oyu should have no cooling probs. currently i am running these same fans with a two row aluminum rad on my really built 440 and have no problems.
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88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 03:31 PM

Thanks 360Duster but that thread was the one that I mentioned was side tracked. The original question was not HP related and I think the originator was a bit peaved that he was not getting an answer to his question.
Jerry, I was hoping to hear from someone that has this set up. Did you notice a big difference when you did the swap? Or was it negligible?

Keep em coming...

Marcus
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-08-2002 03:39 PM

Be carefull with the ratings that the manufacturers give out, as they don't tell you what pressure drop they are at. We tried a 2700 (?) cfm Black Magic fan on the TT340 and it did not do as well as the old dual 12", unshrouded, fans that I took off (rated 2200 cfm). I think amp draw is going to be a better indication of actual air moving power. The Black Magic pulled only 13 amps, the dual 12" pulled almost 30 amps, and the highly touted Spal fans will also pull 30 to 35 amps in a dual 12". You will definitely need an alternater upgrade if you are in traffic much.
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Jerry
Moparts Member
Posts: 1145
From: WARREN, MI
Registered: Nov 1999
posted 07-08-2002 03:51 PM

i did notice a small difference but it was not significant and i would not pay $200 for a set of fans. like i said i bought autozone fans and then made my own brackets to mount them to the rad.
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440Scott
Moparts Member
Posts: 108
From: Manchester, NH, USA
Registered: Jun 2002
posted 07-08-2002 03:59 PM

2500 cfm not much? it is way more than an engine driven stock fan, you could make do with about half that, a 318 is not hard to keep cool. The 2500 setup is for high hp big blocks, You don't need that much fan, a single 14 or 16" will be sufficient. Don't waste your money buying too much fan for your application.
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88Dodge150
New Member
Posts: 25
From: Ashburn, Va
Registered: Jul 2002
posted 07-08-2002 04:04 PM

I am just going by what they(Flex-a-lite) show on their website. Granted it may be a bit much. I would still love an answer to how much CFM is a stock fan worth. Even if the 2500CFM that the 210 is rated for is too mush then I guess it would be better to have too much than not enough right? The other option is to buy a single fan and rig up some mounting brackets and a shroud.... The 210 is right at 200$ but it included the temperature control/AC switch/fans/shroud. So I figured it was money well spent if it did the job I was hoping for....
Please correct me if I am wrong...

Marcus
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-08-2002 04:26 PM

I would have to disagree about how easy it is to keep an engine cool with electrics. I ran electrics on the TT340 Challenger for 12 years, and never was satisfied. It would always get to 220 idling for more than 10 minutes, which I think is too hot for an engine that is thermoed at 180. To make matters worse, the alternater would not keep up, so the voltage would drop, the fan would go slower, the engine would run hotter, etc. We had the ignition shut down several times in traffic because of low voltage/dead battery. It took a 140 amp (80 at idle) GM alternater to be able to run long periods in traffic.
A change from copper radiator to aluminum cooled the engine quicker when moving, but did not do anything at idle.

Using the "wet finger" wind gauge, I would say my clutch fan, running at 1.3 times engine speed, moves about double what the electrics did.

As far as power goes, an electric that pulls 30 amps at 13.5 volts is using about 1/2 hp. If you figure double that to 1 horsepower, and double that again for extra speed before a clutch fan releases, you are still only looking at about 1 1/2 extra horsepower loss, to get double the cooling airflow at idle.

Unless the cooling system is specifically designed for electrics, with very wide radiator and fan coverage (Corvette), in my opinion, electrics are not worth the effort.
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440Scott
Moparts Member
Posts: 108
From: Manchester, NH, USA
Registered: Jun 2002
posted 07-08-2002 04:30 PM

The problem with too much fan, besides cost, is that you may have to upgrade your alternator, noise can be a factor. Stock fans vary greatly, at idle, most stock fans pull less then 1000cfm, they only pull good at moderate/high rpm, but by then your moving and don't need it so much. I'm building a 440 powered street rod, a 16" spal is more than sufficient. What ever you do, don't let anyone tell you need 5000cfm, not unless your want to add some wings and try to fly that thing.
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440Scott
Moparts Member
Posts: 108
From: Manchester, NH, USA
Registered: Jun 2002
posted 07-08-2002 04:41 PM

booster- I don't know anything about your car, but it is widely accepted that electric fans are far more efficient than engine driven, just pick up a any copy of Hotrod, carcraft, or look at what all the high performance guys are doing, the only people I know who run stock fans in high perf cars are the resto crowd.
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booster
Moparts Member
Posts: 999
From: Minnesota
Registered: Mar 2000
posted 07-08-2002 04:57 PM

It is a twin turbo 340 in a Challenger. It is a handfull to cool, but probably no worse than a hot big block.
Most of the electric setups that I have seen, beyond what I have tested on my car, were on drag/street type cars. Many of the owners stated that they were fine in traffic, but when in traffic, most of them got hot and had to stop and cool off. In my opinion, if a car will not stay under 200 degrees, idling for 30 minutes, with the hood down, in 100 degree heat, it is not staying cool enough.

A Spal 16" is a very good fan, and may do just fine for you, depending on how you use the vehicle, but from what I have seen, the downside of the electrics is not worth the gains.

Where did you get the 1000 cfm number?Judging from the airflow I have seen (not actually measured however), I would estimate that a MP clutch fan (non locked) with a 5 blade fan, would be putting out about 4000 cfm at 800 rpm on a 1 to 1 drive setup and about 5000 on a 1.3 to 1 drive setup.

Griffin radiator recommends a clutch driven fan at 1.3 times engine speed, with the proper water pump, for street driven muscle cars.
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440Scott
Moparts Member
Posts: 108
From: Manchester, NH, USA
Registered: Jun 2002
posted 07-08-2002 05:28 PM

booster-In my case I have no room for a engine driven fan, and most of my experience/info comes from the streetrod world, almost no one runs engine driven fans.
I've read quite a few tech articals about fans and it was in one or more of those that the cfm # for stock fans was mentioned, I think its important to note, stock fans vary greatly, your fan sounds very good. One of my older cars came with a 4-blade stock fan, no shroud, it was pathetic. A shroud and a 7-bladed fan fixed that problem. I do agree with you, in that, if a engine driven fan gets the job done, why mess with it? If I had room for one on my car, thats the way I would go.
Twin turbo? Your car must fly!
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plumebody
New Member
Posts: 67
From: rochester ny
Registered: Mar 2002
posted 07-08-2002 06:47 PM

boost and 440scotty, I can use my anemometer to measure the air flow on my viscous fan if you would like. Its a for sure way to tell!
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hemiallen
Moparts Member
Posts: 3494
From: Lodi, CA
Registered: Mar 2001
posted 07-08-2002 07:06 PM

Booster, you lost me on the electric fan / vs hp loss math.
Are you saying you feel a mechanical fan only sucks away 1 1/2 HP from a motor?
Sorry if I mis-understood, but I think a mechanical fan takes more like 10 or 15 hp minimum from tests I have read.
ALLEN
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360duster
Moparts Member
Posts: 671
From: near Omaha, NE
Registered: May 2000
posted 07-08-2002 08:05 PM

Allen: The calculations that I did were based on some very broad assumptions. I first assumed that the clutch fan would move twice as much air as the electric (5000 cfm). I then assumed that to move twice as much air would take twice as much power. Since the electric I used pulled 30 amps, the power consumed was 30 amps
x 13.5 volts = 405 watts. 405 watts X .00134 = .542 hp. Double the .542 and you get 1.084 hp to move the air with the clutch fan. I then assumed that by the time you double the airflow of the clutch fan by increasing engine speed, it will start to freewheel, and not consume any more power beyond that (1600 rpm engine speed). You would then be using 2.168 hp for the rest of your rpm range.
These are very rough calculations, but I think representative of what we are looking at. I will try to pull the old Carcraft article and see if they are similar.

I think the 10 to 15 hp everyone has heard of as loss with a mechanical fan is only for a fixed fan. When you start spinning them at 5-6000 rpm, they could consume big power. If you interpolate my calculations to 6000 [(6000 / 800) X 1.054 ]you would be using 8.13 hp with a fixed fan, if you assume linear power use with speed increase.

I don't know if I made it clearer or muddier!
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hemiallen
Moparts Member
Posts: 3494
From: Lodi, CA
Registered: Mar 2001
posted 07-09-2002 09:20 AM

Thanks Booster, I understand what you had said now. I had made a bad assumption in reference to electric motor hp- where you were talking mechanical HP drag. Sorry.
Makes sense the clutch fan takes less hp than a mechanical fan. I assume the articles I saw were NOT clutch fan numbers.
Thanks, ALLEN
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Electric fan hook-up question

68Bullet
Moparts Member
Posts: 139
From: Oakland, CA
Registered: Feb 2000
posted 05-27-2002 03:06 AM

As an extra cooling precaution for 90 degree stopped traffic (AKA summer), I got a pusher electric fan out of the junkyard. I want to wire it so that it only comes on after a certain temperature, like 210 or something. I know this will involve some sort of temperature controlled switch assembly. My question is, what switch do I get, and where do I stick it?
I was looking to see how the modern cars are wired and it seems most of them have a coolant temp sensor in the radiator. Should I buy a stock coolant temp sensor for some brand x car and wire it in? Suggestions? Thanks
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cam440
Moparts Member
Posts: 1121
From: Citrus Heights,CA,USA
Registered: May 2000
posted 05-27-2002 03:37 AM

Actually it is very simple. You can get a "radiator fan switch" for a 1988 Pontiac Fiero. It will switch at 198°F and is a one wire thermistor. You will wire the fan as follows....
Fused 12v+ battery to "red" fan wire (were the positive fan wire is red)
Then wire the ground wire from the fan motor to the Fiero switch, (which is 3/8 pipe thread). At 198°F the switch will close and complete the ground to your fan motor. If you do NOT want to have the fan stay on when you park, then wire the positive wire to a switched ignition, but to do this, I would run through a standard 30 amp Bosch relay. Hope this is helpful.
-CHAD
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WES HUTCHINSON
Moparts Member
Posts: 195
From: PUYALLUP,WA USA
Registered: Feb 2002
posted 05-27-2002 05:23 AM

Summit sells an adjustable switch that ranges from 170 to 210 I believe. The mercury bulb goes into the upper radiator hose, it has a special rubber gasket that comes with it and goes for around $20.Its rated for enough current for most fans. I would still fuse it though, no need burning down your car on the Dumbarton bridge if you can help it.
wes
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GLENNP
New Member
Posts: 53
From: CLEBURNE TX. USA
Registered: Apr 2002
posted 05-27-2002 10:58 AM

Here is the pt# for the fiero switch, 3040674. I work in the parts dept. at a GM-FORD dealership.
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440 Scamp
Moparts Member
Posts: 510
From: Kirkwod,Illinois
Registered: Oct 2000
posted 05-27-2002 12:12 PM

I always use a relay to switch high current loads like a fan. The switch will last longer too. I had a 71 Charger bigblock cooled by two pushers that were wired with the radiator type sensor. They would run 3-5 minutes after shutdown due to no circulation when not running. It never failed to start but the charging system was always trying to recover the battery. It was also marginal at idle,it needed a larger alternator
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Glen
Moparts Member
Posts: 842
From: Pacific Northwest
Registered: Dec 1999
posted 05-27-2002 01:43 PM

Yeah, I think I'd be inclined to use a relay as well. Just use the thermistor to controll the coil side of the relay. And then run the feed (fused) wire to the fan through the points of the relay. The only real problem is that there's no place to install the sensor in a stock SB chrysler intake. I mean, what is the size of the pipe thread on a stock sender?? 1/4? It's hard to adapt something up from that and still have room for the bottom of the sensor.
Glen
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cam440
Moparts Member
Posts: 1121
From: Citrus Heights,CA,USA
Registered: May 2000
posted 05-27-2002 02:13 PM

Glen, I agree that a stock intake may not have a spot for this sensor, but there are a lot of different sensors out there. Also, I would thin kthat whoever were to use an electric pusher fan would not have a stock intake
I did not wire a relay into mine because the power feed was fused, and the thermistor only controls the ground. Never had a problem....however a realy is ALWAYS better!
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68Bullet
Moparts Member
Posts: 139
From: Oakland, CA
Registered: Feb 2000
posted 05-27-2002 06:03 PM

Thanks for all the input, but 1 more quick question: what is a relay and where can I get one? (you can probably tell by now that I dislike electrical work)
Also, it's a big block, so I will likely try to plug the switch into that square plug in the waterpump housing. And yes, not a stock intake
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ed in VA
Moparts Member
Posts: 430
From:
Registered: Jul 2000
posted 05-27-2002 07:07 PM

A relay is a remote-control switch. It allows you to use a small current to turn a big current on or off. Once you figure them out you'll be using them everywhere :-)
Basically it's a box with 4 terminals. Two of them are the switched terminals, and two of them are the control terminals. For your fan, the power lead for the fan would go into one switched terminal and out the other (just like a plain old switch). The trick is that you're going to operate that switch with the control terminals and another wire from the temperature switch.

Run a new lead from power to one of the control terminals, then from the other to the temperature switch.

Right now your fan goes on when the temp gets hot and the temperature-sensitive switch closes the motor's power circuit.

Here's how it will work with a relay:

When the temperature sensor gets hot, iinstead of completing the power circuit for the fan motor it'll complete the circuit across the relay's control terminals. That allows a little current to flow through an electromagnet inside the relay which pulls the switch to send power to the fan. When the temp goes down, the temp sensor opens the control circuit and the electromagnet lets go of the switch, causing the fan to turn off.

The new lead should be fused, mine shares the fan's fused power but I'll be changing it to run off the ignition switch so that the fan doesn't run when the car's off.
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67 Cuda
Moparts Member
Posts: 359
From: Livermore, CA
Registered: Apr 2001
posted 05-27-2002 07:33 PM

Here is link you might find handy. Instead of the rocker switch, your sensor switch will go there.
http://www.painlesswiring.com/1098relay.jpg
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Runner
Moparts Member
Posts: 2627
From: Lewiston, idaho
Registered: Nov 1999
posted 05-27-2002 07:49 PM

i drew this up a while back, its in the tech archives now. this wiring will give you total control of your fan. you can lieave it on auto, have it on manual on and off. i like this becasue i dont want a fan running while im makeing a pass. plus i sometimes want my fan on. and most of the time i leave it on auto.

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cam440
Moparts Member
Posts: 1121
From: Citrus Heights,CA,USA
Registered: May 2000
posted 05-27-2002 07:59 PM

Hope this helps.

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