What is the correct fan to radiator clearance?

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jawbone

jawbone

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70 340 installed in 68 Barracuda. Installed 68 water pump and low profile Hayden fan clutch. Distance between fan and radiator is 2 3/8 inches. Radiator side of fan is at shroud opening meaning not below outside edge of shroud. Have opportunity at this point before I continue is to install sock Hayden fan clutch to move fan closer to radiator. What do you guys think?

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I'm not sure if "fan to radiator clearance" would be as much a concern to me as the fact the the fan isn't sitting within the fan shroud. The way it is now, with the fan sitting outside of the shroud, you're going to get a lot of "runaround" or "bypass" air, and your cooling efficiency is going to suffer.

In a perfect world (with rainbows and butterflies and unicorns) you could either get a longer shroud, or install a different spacer behind the fan.

But with the latter you will risk running the fan clutch too close to the radiator....

(So I guess "fan to radiator clearance" is the issue after all!)

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ProjectBazza said:
I'm not sure if "fan to radiator clearance" would be as much a concern to me as the fact the the fan isn't sitting within the fan shroud. The way it is now, with the fan sitting outside of the shroud, you're going to get a lot of "runaround" or "bypass" air, and your cooling efficiency is going to suffer.

In a perfect world (with rainbows and butterflies and unicorns) you could either get a longer shroud, or install a different spacer behind the fan.

But with the latter you will risk running the fan clutch too close to the radiator....

(So I guess "fan to radiator clearance" is the issue after all!)

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Thanks for response. If I replace fan clutch for a standard depth, this will move fan deeper into shroud and move fan closer to radiator. At this point do not know how much depth I will gain with standard fan clutch. Am looking into that now.
 
Standard rule of thumb is that the fan blades should be half in/half out of the shroud. I don't think a little further in would hurt, just not further out.
As far as clearance to the radiator goes, I wouldn't get any closer than 3/4-1", but I don't think that'll be an issue with your shroud.
 
2 inches is "too far" to be effective. 1/2" is "too close" — you won't be able to get the bolts in and it may contact the radiator when the engine mounts flex. I think somewhere around 3/4" to 1" is the sweet spot. BTW, it looks to me that you really can't move that particular fan any closer to the shroud — you will risk the fan blades contacting the rim. Think about how when you rev the engine, it rocks to one side. You really would want 1/2" clearance between the blade tip and the shroud rim. Right now your fan only clears because it has the notch in the corner of the blade. If you pushed it in further it looks like you would have almost zero clearance.
 
mvh said:
2 inches is "too far" to be effective. 1/2" is "too close" — you won't be able to get the bolts in and it may contact the radiator when the engine mounts flex. I think somewhere around 3/4" to 1" is the sweet spot. BTW, it looks to me that you really can't move that particular fan any closer to the shroud — you will risk the fan blades contacting the rim. Think about how when you rev the engine, it rocks to one side. You really would want 1/2" clearance between the blade tip and the shroud rim. Right now your fan only clears because it has the notch in the corner of the blade. If you pushed it in further it looks like you would have almost zero clearance.
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You have good observation. The shroud is just resting against the fan for the pic. Thanks for your comment though.
 
Professor Fate said:
Standard rule of thumb is that the fan blades should be half in/half out of the shroud. I don't think a little further in would hurt, just not further out.
As far as clearance to the radiator goes, I wouldn't get any closer than 3/4-1", but I don't think that'll be an issue with your shroud.
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I can get it closer but at the moment do not know the difference between Hayden 2947 and 2747 fan clutches. Thanks for the response.
 
It looks like you have the pre-1970 water pump (and timing cover). If so, then there is no need for ultra compact fan clutch.
The notch in the fan blades helps provide additional clearance to the bubble top tanks (correct for a '68)

The catalogs say overall hts, and distance from pulley to fans are:
2706 3.3", 1.75"
2747 3.3", 1.62" (fan is closer to pulley)
2705 3.1", 1.53" (clutch shorter and fan closer to pulley) [also measured, see photos below]
2947 2.8", 1.08" [measured see photos]
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Mattax said:
It looks like you have the pre-1970 water pump (and timing cover). If so, then there is no need for ultra compact fan clutch.
The notch in the fan blades helps provide additional clearance to the bubble top tanks (correct for a '68)

2706 3.3", 1.75"
2747 3.3", 1.62" (fan is closer to pulley)
2705 3.1", 1.53" (clutch shorter and fan closer to pulley)
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Thanks for the response and information. Do you know how these numbers compare to the 2947. Wanting to know how much I will gain by using the 2747 fan clutch.
 
jawbone said:
Thanks for the response and information. Do you know how these numbers compare to the 2947. Wanting to know how much I will gain by using the 2747 fan clutch.
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My typo. That is 2947, see photo.
edit Let me see if I can check the numbers too.
2947 also requries the reducer bushing- which does not fit snug.
www.forabodiesonly.com

Fan clutch bushing question

That brass bushing that goes in the fan clutch to help center it on the water pump snout is it supposed to be slightly longer than the hole in the clutch itself? I just noticed it while mocking up my aluminum pulleys. The bushing has a split down the length of it but with it sitting in the fan...
www.forabodiesonly.com www.forabodiesonly.com
 
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Hayden 2947, Thermal drive.
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edited my earlier post again.

Found this:
If my notes are correct, the Hayden catalog showed.
1968-73 340 => 2707 thermal, 17107 non-thermal, 2747 Heavy duty
1968-73 318 => 2706 thermal, 1706 non-therrmal, 2747 Heavy Duty
 
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Mattax said:
Hayden 2947, Thermal drive.
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edited my earlier post again.

Found this:
If my notes are correct, the Hayden catalog showed.
1968-73 340 => 2707 thermal, 17107 non-thermal, 2747 Heavy duty
1968-73 318 => 2706 thermal, 1706 non-therrmal, 2747 Heavy Duty
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Wow. Now that's what I need but how do you get your fingers in there. Thanks for the information. I'm going to shoot for the 2747.
 
jawbone said:
how do you get your fingers in there.
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With much difficulty! LOL
The 2947 shorty is definately a choice of last resort. Fortunately I didn't have to go there even with the later water pump and timing cover.
 
And a sheet of cardboard to protect the radiator and hands.

Just don't forget to remove it before you reattach the shroud!
 
I have 3/8s of an inch now, but Thats with a 1 inch spacer, I have a
3/4 inch spacers now, need to put it on when I install my Alternator..
Some good information here in this thread for you :thumbsup:

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memike said:
I have 3/8s of an inch now, but Thats with a 1 inch spacer, I have a
3/4 inch spacers now, need to put it on when I install my Alternator..
Some good information here in this thread for you :thumbsup:

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Some great information.... Have parts on the way. Now if I could get my new voltage limiter working again. The ground screw on the instrument cluster is stripped. Thanks for your response.
 
jawbone said:
Thanks for response. If I replace fan clutch for a standard depth, this will move fan deeper into shroud and move fan closer to radiator. At this point do not know how much depth I will gain with standard fan clutch. Am looking into that now.
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  1. Is the shroud the factory shroud for the car, rad engine combo?
  2. did the car, rad, engine combo originally come with a clutch?
My 67 273 did not come with a shroud and the fan is 1-2 inches from the stock rad. With a stock shroud the fan is about 1/2 in and 1/2 out.


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Dana67Dart said:
  1. Is the shroud the factory shroud for the car, rad engine combo?
  2. did the car, rad, engine combo originally come with a clutch?
My 67 273 did not come with a shroud and the fan is 1-2 inches from the stock rad. with a stock shroud the fan is about 1/2 in and 1/2 out.
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Hi Dana67Dart. Factory shroud for 340 car and radiator engine combo. Can give you the numbers if you want. Car was originally /6 with clutch.
 
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