How many CFMs needed from electric fan??

[BLOZ UP]

As for the comment 'coverage is more important than CFM'---I'll call BS on that one! I had twins at X CFM on mine, and it overheated. I replaced it with a larger single leaving FAR more uncovered surface and it cooled just fine with X+ CFM. Later I went back to a dual fan setup for 'staging' of the fans and kept the same CFM as the single...still no problems to date and that was years ago!

 

You can cover the entire radiator, if that fan does not move sufficient air it WILL overheat.

 

If you don't cover the entire radiator, but have sufficient CFM it WILL NOT overheat.

 

If you have a fan with a certain CFM covering only part of your radiator, and then add a shroud it will cool better. You can have a million CFM but if it's only covering 1/10 of your radiator it's going to overheat.

 

I suppose you're right though, coverage isn't more important. It's equally important.

[bjhines]

http://www.mouser.com/ProductDetail/Tyco-Electronics/V23134J1052D642/?qs=sGAEpiMZZMtSzCF3XBhmW%2foU1yPuOCZA7Rkc%252bhjhbI8%3d

$10 TYCO Power relay F7 series, number V23134-J0052-X429. Ford(focus ZX3?), Mercedes(midsized sedans), Dodge(?), etc all use them for starter relays(they sell for $50 as factory replacements). I also like the F4 series but high ambient temps will reduce capacity by 25-30%(which is less than required by the high speed wire).

 

The relays do not "burn up". They do not even get hot. The contacts get dirty and they fail to switchover or activate. Tap on the relay and/or cycle it a few times and it might clear up... temporarily. Once you get a resistive connection the relays WILL BURN UP. You will have relay failures at a fraction of the rated cycles when improperly applied. Most of these relays are rated at 100,000 cycles. I'll be you don't get 10% of that before failures. The only argument FOR ignoring proper circuit design is acceptance that the relays are incredibly long lived. You might not see 1% of it's rated cycles before you build another hotrod. Many people have blamed cheap relays for certain manufacturer's fuel pump and other issues. It is more likely power circuit design not relay design.

 

I have had fan relays fail. It really sucks when you can't run to the Walmart fog light shelf and get a new one. Dual fans will work with foglight relays. The sockets for high current relays are also unique because of their 3/8" spade terminals. This also makes it hard to get a replacement to fit unless you can find it at the Ford or Mercedes dealer.

Edited December 11, 2010 by bjhines

[Tony D]

By no load what does that mean? No fan and freewheeling the motor? That, I find an odd statement indeed!

 

Especially restricting flow decreases load, and increasing flow increases load---you got that one backwards! Put a line amp clamp on your fan and observe the amps, the cover the radiator with some cardboard---you can almost hear the motor speed up. Cavitation of flow results in a precipitious drop of amperage.

 

Amps=Flow

 

Running with no flow across the fan, the motor should exhibit a much lower amperage than when spinning a fan and moving air.

[bjhines]

Tony,

I thought I remembered the same thing. But I would refrain until I tested again. The Spal fan appears to show the opposite on their data sheet.

Edited December 11, 2010 by bjhines

[datsun280zx]

Thanks for all the help guys. So i can figured out what to buy now and made a wiring diagram for this. Lemme know if you see any problems with it. I made it so when i turn the car on the low speed(PURPLE) will automatically turn on and ill have the switch to turn on the high speed(ORANGE) So i figure my to buy list is a fan from a 93-95 taurus, 70 amp relay( just to stay on the safe side), a switch, and a couple a fuses. Lemme know if i forgot anything lol have the feelig i did. Thanks again guys!

[bjhines]

That is not gonna do it.

 

You need the ignition source and toggle switch powering the 86 terminal through the coil and out 85 to ground. Many relays have diodes in parallel with the coil so it is important to make 86 the 12v input and 85 the ground.

 

The BATT source goes to terminal 30.

 

87a as low speed and 87 as high speed are correct.

[datsun280zx]

Hmm i figured that id hook 30 up to one of the power wires on the ignition so that when i start the car the low speed turns and then have 85 to the battery with a switch so it would turn on the high speed when i flip the switch on. I think i got it, dont get much sleep anymore

[Tony D]

Two switches, separate circuits and relays. Low speed fan comes on at 170F (with 160F thermostat), High fan comes on at 180F

 

Anything later than that, and likely the head will have 'runaway' going on with steam bubbles forming and insulating the cooling system (see KTM's comments on the matter.)

 

Most people don't understand that on most cars once the temperature reaches around 180F 185F there are steam pockets already forming in the head which make it almost impossible to 'catch up' regardless of the fan CFM or huge-o-matic radiator. To combat that you either need to increase block pressure (speed up pump) or run a higher static pressure (24# cap).

 

You will find 'troubled cooling systems' seem to become 'trouble free' if you don't get them to the steam-pocket formation temperature. If you do intend to run 180F thermostat or above there for a fan cut in, do yourself a BIG favor and get a 24# radiator cap!

[Tony D]

If you have a fan with a certain CFM covering only part of your radiator, and then add a shroud it will cool better. You can have a million CFM but if it's only covering 1/10 of your radiator it's going to overheat.

 

I suppose you're right though, coverage isn't more important. It's equally important.

 

Despite the contentions here, I'm going to say 'WRONG' again.

 

If you cover 1/10th of the radiator surface and effectively force all the CFM through that equally across the radiator in the direction of flow you will cool the engine.

 

Your example is ludicrous on it's face, and having a shroud has nothing to do with it. It is NOT a necessary addition to a properly sized fan.

 

A shroud HELPS efficiency, but is not REQUIRED.

 

As I said in the original post you objected to: IF YOU DON'T HAVE ADEQUATE CFM YOU WILL OVERHEAT. (A shoroud will NOT change that fact! If you have MARGINAL flow, a shroud may prolong the agony but will not FIX anything!)

 

I stand by that statment.

 

For an equally ludicrous rebuttal to your million CFM 1/10th coverage example I proffer this:

 

100CFM Bathroom Exhaust Fan, FULLY SHROUDED TO THE RADIATOR WITH 100% PASS THROUGH AND NO LEAKS.

 

This car will overheat. It will likely overheat at idle even at temperatures down to 40F due to insufficient flow across the radiator.

[BLOZ UP]

Despite the contentions here, I'm going to say 'WRONG' again.

 

If you cover 1/10th of the radiator surface and effectively force all the CFM through that equally across the radiator in the direction of flow you will cool the engine.

 

No, not going to happen. I'm not sure what you were trying to weasel in with that "equally across the radiator", but if you do not have enough coverage you will not cool the engine no matter what the CFM.

 

Your example is ludicrous on it's face, and having a shroud has nothing to do with it. It is NOT a necessary addition to a properly sized fan.

 

Right. Properly SIZED fan, that's what I was getting at. I would get a 16" fan over a 12" fan each at K CFM.

 

A shroud HELPS efficiency, but is not REQUIRED.

 

I never said it was.

 

As I said in the original post you objected to: IF YOU DON'T HAVE ADEQUATE CFM YOU WILL OVERHEAT. (A shoroud will NOT change that fact! If you have MARGINAL flow, a shroud may prolong the agony but will not FIX anything!)

 

And as I said, but not in all caps: "If you don't have adequate coverage, you will overheat."

 

For an equally ludicrous rebuttal to your million CFM 1/10th coverage example I proffer this:

 

100CFM Bathroom Exhaust Fan, FULLY SHROUDED TO THE RADIATOR WITH 100% PASS THROUGH AND NO LEAKS.

 

This car will overheat. It will likely overheat at idle even at temperatures down to 40F due to insufficient flow across the radiator.

 

Right. So, a 3000 CFM fan with, again, a fraction of coverage will also overheat. I'm glad we have come to an understanding. That doesn't seem so ludicrous to me. But proffer whatever you have to proffer so you can increase your internet ego.

 

I never said that you could run whatever CFM as long as you had a shroud. I originally said that coverage was more important. However, I decided that I was wrong, and that it's equally important.

Edited December 21, 2010 by BLOZ UP

[Tony D]

"Right. Properly SIZED fan, that's what I was getting at. I would get a 16" fan over a 12" fan each at K CFM."

 

12 or 16" will not make a difference. I ran dual 10's or single 16, 14 or even an HE 12"...they all worked if they had adequate CFM.

 

All worked WITHOUT shrouds.

 

Adequate 'coverage' and adequate CFM are entirely unrelated and different things. As noted above, dual 10's, single 12, 14 or 16 all worked adequately to cycle the fan on and off and not allow an overheat to exist. This was on a 350HP turbocharged 1973 Z in 110F+ Desert Heat with a 3 core radiator. If 'coverage' was all that important (or moreso than CFM) then at some point the smaller fans would not work. They did. Coverage with any fan (I might be so bold as to say a single 10" would work, but I haven't seen one with adequate CFM---and putting a shroud on it won't help if the CFM ain't there!) You won't overheat if you have CFM. You can have all the 'coverage' in the world, if there isn't enough CFM flowing (shrouded or not) you will overheat. Been there, done that...

 

Run a strip of duct tape across the radiator at the top. Now, do it at the bottom.

 

Repeat until you have approximately 3/4 of the radiator is covered.

 

Now go driving without a fan at 30mph in fifth gear. See where the temperature equalizes at, then repeat at 60mph and report the results.

 

Air flowing equally across the flow direction of the radiator needs VERY LITTLE space to adequately cool the engine.

 

If you can cool a 400HP L6 with a condenser core from a 74 Chevrolet Impala...

 

Don't know where you got the idea that 'coverage' is anywhere near as important as CFM. I have run 16" fans and overheated. Arguably they cover more than the 14" that I replace it with (and which was on previously without overheating)---the only difference was CFM. Don't take it to a ludicrous end to make a bad point. We're talking about commonly available fan combinations, and dual 10's will work, so will a single 12 if the CFM is high enough. I know, I've done it on more than one car, with pretty extreme operation requirements in a Z car.

 

If I can see instrumented changes when I change appearance pieces on the front of my car, I think I can tell if a fan is adequate or not with the same instrumentation...

[bjhines]

You guys are crazy... I mean that in a good way. THERE ARE BIGGER FISH TO FRY!!! You both agree that a decent fan and a decent shroud are the way to go. FINI!

 

I designed a circuit to use a 3/8"NPT sender to automatically switch the 3-state(OFF/LOW/HIGH), 3-wire Ford Taurus fan. I have an AC-full-on input, and I have a relay output for a second fan. I have a dozen mosfets in paralell on the bench trying to reliably PWM control this beast(heatsink and heatsink cooling fans are too damn big and expensive though).

 

Through all of this design work I keep wondering just where the best location for the sender is, and what temperature parameters are best. I placed MY sender in the top of the water outlet, but I am not married to that position. I considered placing the sender in the radiator outlet. I decided to have the fan sender very close to my gauge sender. The fan sender is on the cool side of the thermostat while the gauge sender is just below it on the hot side of the thermostat.

 

My settings so far are based on what I have found avaiable from aftetmarket suppliers. Low temp(185F) thermostats will use lower ON-temp settings for electric fans. High temp(195F) thermostats will use higher temp ranges for the fans. Most of the aftermarket controllers have OFF-states that are 15-20 degrees cooler than the ON-state. This temp range is built into the fan "switches" with only 20% accuracy. I developed my circuit to mimick this behavior with much greater accuracy, precision, and adjustability.

 

I can see changing the location of the sender GREATLY changing the requirements for both ON-state and OFF-state settings. My next design will get even better with a Schmitt Trigger/comparator. I used Zener diodes in the first design, but they are prone to wander as ambient temps vary greatly underhood.

[Tony D]

"You both agree that a decent fan and a decent shroud are the way to go. FINI!"

 

If that was what was said, I would agree. The reason I'm a stickler on CFM is that I bought the lie ONCE that 'more coverage is better' and bought (as stated) a 16" fan rated to be 'adequate' for my application.

 

It was not. It didn't cool as well as my 'smaller' 14" fan. And therein lies the rub. It started quite a bit of experimentation where I determined that the 'size' a company put on their fans has very little to do with how they cool.

 

What IS very applicable is the CFM. And as you mentioned earlier, the AMPS are directly related to the CFM a fan produces.

 

I don't want anybody else to waste money on a fan that is 16" thinking that they will help their situation simply because 'coverage' is better. If the fan is not capable of moving the air necessary (see my original posted comment which was disputed) then it won't work...period. Regardless of what you want.

 

I didn't have to make a ridiculous example to make a 'theoretical' point, I stuck to real world sizes and examples which are known and proven to work. Experiments which proved that the 'coverage' as a portion of radiator covered is basically irrelevant---it's the CFM that counts! A 12" 5500CFM fan will work just as well as a 16" 5500CFM fan. Packaging a tight engine bay will benefit from the easier placement of a single 12" as it can 'move' quite a bit on the radiator. Split the difference and get a pair of 2500 10" fans, it's all good. None of them 'needs' a shroud, it might boost effectiveness, but I haven't personally had an issue where I needed a shroud to have the engine operate in the proper temperature ranges I desired (following the CFM guidelines I gave above!)

 

Main point being (and my duct tape example was designed to have someone check their own example) is that the radiator needs very little actual airflow AREA to accomplish what it needs to do. Unfortunately it was not checked. Don't know why.

 

As to switch requirements, I like the Hayden or other 'adjustable' electronic controllers where I can adjust a trimpot to get actual fan on/off temperatures to work where I want them. Were I more ambitious (and if JeffP had more time) I would de-pot their black box and make a multiple circuit to control multiple fans from several different temperature ranges.

 

Right now, I run a single 10" (around 2500CFM) which has a second 10" cycle on if the temperature goes much above 180. First fan is on at 175, second at around 180. On colder days (below 40F) I only run one 10" fan. In July driving in Phoenix in 120F heat, if I am below 25mph one fan is on, and when I come to a dead stop in traffic, the second fan cycles on/off on a 180on 170off cycle. First fan comes on at 175 and shuts off at 165. Thermostat is 160. In temperatures below zero, I can have issues getting to operating temperature and kick myself for forgetting to install the 180F thermostat before going to the cold places...but that hasn't happened in a while.

Edited December 23, 2010 by Tony D

[Tony D]

I'll also point out that the Thread Title was 'How many CFM's are needed from an electric fan?'

 

I believe I'm the only one who justified his answer for what he gave...

 

What is the CFM of the Taurus Fan? A draft gauge and sq ft of coverage will tell you quite clearly what it is...

 

Wanna lay money it compares favorably to what I've posted?

[Miles]

Tony

 

Can you post some pictures of your dual fan set up?

[Tony D]

Nothing spectacular, two 10" fans rated at 2500 or 2550CFM (it's been almost 15 years now!) mounted to the back of the radiator with the standard 'pushthrough' connectors in a 'draw-through' configuration down as low as I could get them. No shroud. It let my water pump pulley stay where it was, and doesn't interfere with my crankshaft damper. My 14" was offset towards the left side of the car as were the smaller ones I tried. The biggest pain at the time was there weren't a lot of 'thinline' fans available like now---and mounting the larger fans got the motor closer and closer to the rotating water pump pulley.

 

I like the idea of dual-aftermarket fans as if one fails, you still have some chance to make it to the side of the road in stop-n-go and get to someplace to affect a repair. With a single...well...

 

Call me paranoid, but I don't like aftermarket fans, have had some fail. I would say the Taurus fan being a single, but OEM tested and proven would be an exception to my paranoia. But as documented there are 'hairs' attached to running a fan that REALLY moves the air it's supposed to (high amperage, etc...)

 

Twin fans won't use less energy, but their individual loads may be more managable without specialized componentry.

[Tony D]

curiously, there are some numbers listed for the Taurus fan online:

 

2500/4000+CFM!

 

Don't know where they get their numbers, but it's interesting that the fan claimed to work the best is right within 500 CFM of my admittedly conservative estimation!

[bjhines]

Tony,

I will disagree with you on your priorities of importance. Your poorly shrouded examples are going to allow some very hot water to pass to the outlet. Is that really desireable?? I dont think so.

 

I look at OEM design with great respect. I can think of a few modern improvements that have made it into nearly every car on the road. We can use some of them on our cars and fan shrouds are easy and proven to work.

 

Higher coolant temperature(there are a lot of reasons this is GOOD, not just emissions related)

Higher coolant pressure(steam bubbles)

constant metered bypass into the recovery tank.(air/steam expulsion)

optimized coolant volume(smaller engine volume, smaller radiator volume, smaller port and hose volume)

optimized coolant flow(hotter cylinders and exhuast passages with cooler intake passages)

optimized cooling fan control(I am playing around with this right now)

optimized aero effects on radiator airflow(in the front clip, FAN SHROUD, underbody, and engine bay)

optimized engine control systems for more consistent thermal demands.

 

 

There are better things to discuss besides how you can get away with no fan shroud or not.

Edited December 24, 2010 by bjhines

[hoov100]

I run a little 3k CFM fan with no shroud on my circle track car without a problem. But we also seal every tiny little hole in the air box. I think there are a couple more important factors to look at when looking at airflow to and out of the radiator, like a sealed airbox, radiator cooling fin orientation, fan shroud, fan blade geometry and construction...etc I feel that we are just in a pissing contest at this point. A fan that has the ability to pull the correct amount of air to keep engine temps nominal is the correct fan.

[Tony D]

"Your poorly shrouded examples are going to allow some very hot water to pass to the outlet."

 

Will it? What is the lower tank's function? The trick is delta rise across the engine to be less than delta T across the radiator. As long as the rejection is higher than input, you are O.K... That some 'hot water bypases' is immaterial as long as the temperature into the engine is low enough to not cause a spot boiling problem in the engine and the resultant runaway issues.

 

My experience has shown that if you insist on running 185F thermostats you will need to run elevated cap pressures or risk runaway conditions (especially in the back two cylinders). For most people it's easier to simply keep the temperature lower and avoid it with standard parts than buy the cap and worry about the leaks on a street car.

 

Let's not get into track modifications for the street. If we want to do that, let's start another thread. Remember I was the guy who mentioned cooling a Z with an Impala A/C Evaporator Core....(what was that about coolant volume optimization again?)

 

The original post asked how much CFM and gave an example. I gave a CFM, gave a reason why it was a conservative and proven number and thought it good enough. Then it digressed.

 

The Z had a Shroud in JDM, it didn't have one here. Some places needed it, cooler places didn't. If the fan produces enough flow the shroud is not necessary. I never said 'don't put one on' conversely I didn't say you have to have one, either.