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Old 06/03/13, 09:07 AM   #1
bronconut73
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How did you do that?

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radiator to fan clearance

If the fan is real close to the radiator will it pull more air through it?
I thought I had also heard that the fan blades should stick out the shroud by about a third.
My blades are not sticking out past the shroud by a third but they are sticking out a little.
My fan is about an inch or so from the radiator right now.
I am not overheating but if I let it sit still for about 30 minutes with the a/c on it gets close to 220F. Never boils over or acts hot. But 220F is a little hotter than I would like.
It is hot here now (90F) but it will be (99F) here in a month or so.

73 Wagon, 3.5" sl, long RS9000's, BC F-250 mounts, WH 1" bl, 33" BFG MT's, C-4, TBP twin sticked Dana 20, P.S., built 351W, Detroits and G2 4.11 gears, front & rear WH axles, Yukon Super joints, BC 4 wheel disc, BC Vintage a/c, WH Procar 2000 seats, Alpine/Pioneer, Cobra 148 GTL/Texas Star.
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Old 06/03/13, 09:58 AM   #2
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Bump....

73 Wagon, 3.5" sl, long RS9000's, BC F-250 mounts, WH 1" bl, 33" BFG MT's, C-4, TBP twin sticked Dana 20, P.S., built 351W, Detroits and G2 4.11 gears, front & rear WH axles, Yukon Super joints, BC 4 wheel disc, BC Vintage a/c, WH Procar 2000 seats, Alpine/Pioneer, Cobra 148 GTL/Texas Star.
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Old 06/03/13, 10:18 AM   #3
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I doubt it. Look at an A/C compressor for your house. The fan is on top of the unit while the coils are on the sides. Plus if you get it close and the body flexes on the frame, or the engine flexes on its mounts you could have the fan grind right into the core (the motor is on the frame and the radiator is on the body.) You want the back of the fan OUT of the shroud to disperse the air pressure. Try sealing up gaps between the shroud and radiator so that the air it's pulling is being pulled through the radiator.

The fan will also pull more air with more RPMs. Since you're idling, it's not drawing a lot. If you do this on a regular basis you might want to add an electric to the front.

"If you don't stand for something, you'll fall for anything"

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Old 06/03/13, 11:24 AM   #4
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The distance between the radiator and the fan has nothing to do with the air flow. Just look at a '72 Monte Carlo shroud. The fan is a long way from the radiator. The amount the fan is inside the shroud may make a difference though. I like to have the fan about half way in the shroud.
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Old 06/03/13, 03:55 PM   #5
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A prop fan will flow more air with a properly sized shroud, it helps control recirculation at the blade. Running the back end of the fan is mostly an automotive thing, in the ventilation world prop fans that are expected to meet a specified airflow will be completely shrouded. Setting the back of the fan out of the shroud allows the fan to "sling" air outward which increases air flow since otherwise the fan would be pushing all the air against the engine. The further the fan is from an obstacle the less this matters.

I have been running off road vehicles for over 30 years with an inch or less of clearance between the fan and the radiator. the reason used to be because I didn't run a shroud and the proximity to the radiator increased actual airflow through the radiator when a shroud was not used. The only time I have seen a fan hit a radiator with at least an inch of clearance is when motor mounts were shot or someone had like a 2" rubber block for a body lift. The motor mounts and 1" rubber body mount physically cant move an inch unless something is worn out, loose, or you hit something running like 50MPH. Then the radiator isn't really a concern. If you are going to off road it that hard then bolt it with solid steel or aluminum spacers.

I hard bolt my bodies with metal spacers for any of my all off road vehicles anyway. Never noticed an adverse affect on ride quality. I ran a Jeep with a Chevy 350 for 20 years with 1/2" clearance. my body was welded to the frame and the engine had 1/4" rubber pads with bolts passing through with little or no clearance. Believe it or not you wouldn't have know from the ride and I never had that fan hit the radiator and it was wheeled hard.

71, 393 roller cam EFI, 700R4, D44, F9, ARB front and rear, on board air, Twin Stick, Cruise Control, P255/85/16 BFG M/T, Custom Plate Bumpers, spare tire carrier, custom floor, 2 inch susp, 2 inch body lift, Blah, Blah, Blah.
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Old 06/03/13, 04:08 PM   #6
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Quote:
Originally Posted by blubuckaroo View Post
The distance between the radiator and the fan has nothing to do with the air flow. .
Actually..yes it will make a difference. If the fan is too close to the radiator, that will reduce the effectiveness of the fan considerably. The farther away the fan blade is from the radiator, the better, assuming of course that a properly fitted shroud is in place. No shroud...all bets are off as you have lost control of where the air comes from and where it ends up going.

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Old 06/03/13, 09:42 PM   #7
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Boy this is the 1st one of these questions we've had this warn season. I guess hot weather has started..
.. I Say the fan needs to be 1/2 in and 1/2 out of the shroud. And as one of the other OF's said. Stop up any gaps you can find. I used some foam rubber strips to stop up the gaps in mine. I took it for about a 40 MPH run maybe 5 mile an got home. Nothing I'd put in it was still there. It has sucked every thing out. It was open again.
... I used spray foam Insulation to seal the gaps around my radiator.
.. Dodge uses that air dam in under the bumper an that'll help.
... BUT Force every drop of air thru the radiator .. It can not go anywhere else. BUT THRU THE RADIATOR. Think this way.

............R. I. P. H. D. May 2nd 1999
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Old 06/03/13, 11:46 PM   #8
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Mine had two 3/4 spacers then the fan when I bout it and was really close. Only down side is if you fourwheel this can happen! I moved my new fan back as far as I could now and have about an inch and a quarter clearence.
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Old 06/04/13, 02:29 PM   #9
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Quote:
Originally Posted by 00gyrhed View Post
...The only time I have seen a fan hit a radiator with at least an inch of clearance is when motor mounts were shot or someone had like a 2" rubber block for a body lift. The motor mounts and 1" rubber body mount physically cant move an inch unless something is worn out, loose, or you hit something running like 50MPH. ...
You didn't mention the dreaded water crossings.
That is one of the more common warnings with regard to how close the fan blades come to the core. About the only time I've heard of fans hitting radiators was with deep water forcing the blades to do things they weren't intended to do.

Residential A/C compressors are "ducted" anyway, even if they don't appear to have what we would refer to as a shroud. The containment case is designed to promote as much air flowing over the coils as can reasonably be had I'm sure.
And they don't usually have to work in a consistent 40 to 100 mph breeze either. I would think that alone could make a dynamic change in how a fan blade acts at different distances from the core, and with different spacing within a shroud. At least with regard to turbulence and cavitation and stuff like that.

The shrouds on an automobile give the air a better chance of flowing more equally over the core fins-n-tubes, and give the designers more leeway in how they mount a mechanical fan over the water pump bearings.
There's only so far you can hang something out before the bearing life suffers.
Under normal circumstances a fan can likely pull enough air over enough fins to do the job of cooling adequately even without a shroud or with regard to distance from the core.
But when every molecule counts, some layouts are just more efficient than others.

Look at any modern car with electric fans and you can see they are often very close to the fins. Fractions of an inch in some cases. But the ducting and shrouding helps promote airflow over all the fins anyway.
Different blade designs usually too though, so you can't necessarily use them as a guideline to where to mount a mechanical fan blade in regard to depth in the shroud.

My .03

Paul

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Old 06/04/13, 02:37 PM   #10
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Quote:
Originally Posted by bronconut73 View Post
If the fan is real close to the radiator will it pull more air through it?
I thought I had also heard that the fan blades should stick out the shroud by about a third.
My blades are not sticking out past the shroud by a third but they are sticking out a little.
My fan is about an inch or so from the radiator right now.
I am not overheating but if I let it sit still for about 30 minutes with the a/c on it gets close to 220F. Never boils over or acts hot. But 220F is a little hotter than I would like.
It is hot here now (90F) but it will be (99F) here in a month or so.
You may be stuck with the location of the fan anyway. A lot of Broncos don't have the leeway to move certain fan designs any closer to the engine because then the blades hit the pullies or other accessories.
With yours having A/C, and maybe P/S(?), you likely have plenty of belts and pullies to contend with. And, unlike blubuckaroo's Monte Carlo pictured , you don't have much room on an EB, between the front of the engine and the back of the core to move things around.

If you can't move the fan back, you would have to trim down the shroud to get the normally recommended fan depth. But is it needed? Hard to say if that's even the cause of your heating up. With A/C running and a hot-ish day, that might be just what it's going to run at idle.
Only experimentation or engineering will tell for sure.

So does yours have a spacer behind the fan? If you reduce it's size or remove it completely, will it work? Or would the fan blades start to hit things before that?

I agree with the sealing methods first though. Make an EB more efficient than it came from the factory. Block off flow between the grille and core support, between radiator tanks and core support, and top of radiator and core support.
At least let the fan and existing shroud work to their best effect as they are before you have to try to re-engineer things.

Good luck. Like you said, it's not overheating, but it's nice when you can keep it farther away.

Paul

'71 Wagon, 3.5" lift, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers.
Soon to be 5.0 w/ NV3550 and NP241 and whatever other parts are stuffed in the cab, storage room and garage, waiting to be installed.

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Old 06/04/13, 05:31 PM   #11
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Fan half in and half out is what I try to attain with a Fan shroud.

351w, F250 serpentine, 1/2" Fan Spacer. I have about 1 1/2" clearance.

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Old 06/04/13, 07:41 PM   #12
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I am O.K. with the fan being 1/2 in/out but for my money we always rec. at least 1" between fan and radiator.the body and frame flex separately and with less the fan and radaitor will get together. !/8" off the a/c works but we have gone to the trouble of loosening engine and body mount bolts. to get that but we don't damage radiators any more.

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Old 06/04/13, 08:06 PM   #13
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Nice to hear from you Chuck.

73 Wagon, 3.5" sl, long RS9000's, BC F-250 mounts, WH 1" bl, 33" BFG MT's, C-4, TBP twin sticked Dana 20, P.S., built 351W, Detroits and G2 4.11 gears, front & rear WH axles, Yukon Super joints, BC 4 wheel disc, BC Vintage a/c, WH Procar 2000 seats, Alpine/Pioneer, Cobra 148 GTL/Texas Star.
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Old 06/04/13, 08:55 PM   #14
Pa PITT
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.......
I agree with Chuck.. Many years ago I built a 440 auto in a one ton truck for a pull & farm truck .. MY 1ST Dodge .. It might have had 50miles on it. I had a brand new 4core radiator .. I had stuck that fan about 1/2 inch from the radiator .
... Well I pulled into a new field of round bales I'd bale the night before .. I had a couple of my boys with me .. They were about 14 & 10. So I pulled up to one of the brand new 1800lb rounds bales. Put the bumper against it an gave it a big push thinking how the Boys would laugh for years about how that bale rolled down the slope.
INSTEAD .. they laughed at the FAN GOING THROUGH PaPitt's new radiator.
... Damn It Boys it ain't funny...

............R. I. P. H. D. May 2nd 1999
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Old 07/24/13, 02:18 PM   #15
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Hi Paul,

Quote:
Originally Posted by DirtDonk View Post
You may be stuck with the location of the fan anyway. A lot of Broncos don't have the leeway to move certain fan designs any closer to the engine because then the blades hit the pullies or other accessories.
With yours having A/C, and maybe P/S(?), you likely have plenty of belts and pullies to contend with. And, unlike blubuckaroo's Monte Carlo pictured , you don't have much room on an EB, between the front of the engine and the back of the core to move things around.

If you can't move the fan back, you would have to trim down the shroud to get the normally recommended fan depth. But is it needed? Hard to say if that's even the cause of your heating up. With A/C running and a hot-ish day, that might be just what it's going to run at idle.
Only experimentation or engineering will tell for sure.

So does yours have a spacer behind the fan? If you reduce it's size or remove it completely, will it work? Or would the fan blades start to hit things before that?

I agree with the sealing methods first though. Make an EB more efficient than it came from the factory. Block off flow between the grille and core support, between radiator tanks and core support, and top of radiator and core support.
At least let the fan and existing shroud work to their best effect as they are before you have to try to re-engineer things.

Good luck. Like you said, it's not overheating, but it's nice when you can keep it farther away.

Paul
I hope this isn't considered hijacking.

I bought the Wild Horses (Ron Davis) fan shroud two years ago. It's a nice shroud. It fit well to the radiator, and the clearance with the fan was good considering the 2" body lift.

A year ago a couple old-timers in Moab were looking at the motor and commented about the fan being too deep into the shroud. They believed that the fan being too deep in the shroud would cause cavitation and reduce the effectiveness of the cooling. At present, the rear of the fan blades is about flush with the back of the shroud.

I decided to change the depth this year. After looking at it more closely, I only have about 1/2" between the back of the fan blades and the upper radiator hose. The spacer between the fan and the water pump pulley looks to be 1". I searched around a little and found one source for a 3/4" spacer; but, I'm really not sure how much that will gain me. I think going to 1/2" spacer would be asking for trouble with any flexing of the fan blades.

The other option is cutting the back of the shroud to about midpoint on the blades. I hate messing up such an expensive shroud when I don't know that it will really help. I have been chasing slight overheating issues the last two years... probably of borderline concern.

I'm just curious if anyone else has run into a similar problem, and if they ended up cutting the shroud.

Any advice will be appreciated.

Thanks

Jeff

1971 Bronco Sport - 302 Running Propane w/ASME Vapor Box Tank
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