Fan shroud question

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akrateffil

akrateffil

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Hey everyone, I'm having some overheating issues on my 69 Barracuda. My car has a 69 440 automatic, with the 484 purple camshaft. The radiator is a aluminum two row that measures roughly 4" thick. I use a mechanical fan. I have fabricated a fan shroud which extends to about 2" ahead of the fan belt. I suspect a timing and/or fuel adjustment problem to be causing the overheating.
My question is; is it possible to have too long of a fan shroud? I'm wondering if the engine is restricting the air flow of the fan. If so I may trim an inch or two from the shroud's trailing edge. I have attach two pictures of what I have.
Thanks,
Andy
 

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To me it looks like the shroud only allowing the fan to pull air from that portion of which is shrouded. Your corners aren't getting pull through? A shroud should also only cover have the width of the fan blades ideally. I'd pull the shroud off and test it. Better? Worse? Same? Then go from there. Fixed fan or clutch fan? How close is the fan to the radiator? I've dealt with same issues. Best thing I did was get a good clutch fan. Even without a shroud it sucks a towel onto the grill at idle! A factory style shroud I picked up will help keep things even more stable.
 
Beatnik said:
To me it looks like the shroud only allowing the fan to pull air from that portion of which is shrouded. Your corners aren't getting pull through? A shroud should also only cover have the width of the fan blades ideally. I'd pull the shroud off and test it. Better? Worse? Same? Then go from there. Fixed fan or clutch fan? How close is the fan to the radiator? I've dealt with same issues. Best thing I did was get a good clutch fan. Even without a shroud it sucks a towel onto the grill at idle! A factory style shroud I picked up will help keep things even more stable.
Click to expand...

I have a mechanical fan, 5 blade 18". There is about 2-3" between the fan and radiator. I had a factory style shroud that did not fit the radiator, so I made one to better fit the radiator and fan location.

The car gets hot at idle, I do not have a temperature number as the factory gauge doesn't show a number. The radiator does spew coolant out the cap (which is brand new). The overheating issue I contribute to timing and fuel adjustment. As I work at getting the motor timed, the air coming from the fan/radiator is incredibly hot. I cannot turn the distributor while it is running due to the air burning my hand/arm. I am wondering if this heat is harming my coil, distributor, and carburetor.

Thanks for your help,
Andy
 
The 383 in my 65 C-body doesn't put out terribly hot air at idle, normally, and no problem holding the distributor. It has just a clutch-fan. That is with the original copper radiator (re-cored). I currently have an alum radiator, but haven't driven that on a hot day. I have had problems with over-heating when it has run lean (I think). It both boiled over when shut off and I recall the distributor and York AC compressor was too hot to hold. I found that happens when the Holley Pro-jection 2D box on it over-heats, especially if sunlight hits it. Then it starts missing fuel pulses. I suggest continue checking your carburetor and searching for vacuum leaks. That hot cam certainly won't help at idle.
 
akrateffil said:
I have a mechanical fan, 5 blade 18". There is about 2-3" between the fan and radiator. I had a factory style shroud that did not fit the radiator, so I made one to better fit the radiator and fan location.

The car gets hot at idle, I do not have a temperature number as the factory gauge doesn't show a number. The radiator does spew coolant out the cap (which is brand new). The overheating issue I contribute to timing and fuel adjustment. As I work at getting the motor timed, the air coming from the fan/radiator is incredibly hot. I cannot turn the distributor while it is running due to the air burning my hand/arm. I am wondering if this heat is harming my coil, distributor, and carburetor.

Thanks for your help,
Andy
Click to expand...

Hmm...of hand I'd say try a spacer to get that fan closer to the rad and re-try the factory shroud. Just seems like it's not sucking air through. If you hold a shop towel infrint of the grill does it pull it in and stick? Should...mine does with my clutch fan and no shroud!
 
We need another angle of the shroud.

The first thing that I see is your fan is too deep into the shroud. There is a spec used for engine cooling called FOOS (Not Chip Foose), but it stands for Fan Out Of Shroud. It is the amount of the depth of the fan that overlaps with the fan shroud. For best performance you want the depth of the fan half way into the shroud and half way out of the shroud. 50% +/- 20% is the best. You can trim back the shroud or move the fan to correct.

Also how well "sealed" is the shroud. Can air get around the fan and/or shroud. You want the shroud to work as a nozzle to help pull and direct the air to flow THROUGH the radiator, not have any paths AROUND it.
 
take the spacer off the fan. replace rad cap with one of a higher poundage. replace themostat with one around 180. replace upper hose with a smooth one and the bottom one too, I can't see it in the pic. get a catch can on the radiator.
 
krazykuda said:
We need another angle of the shroud.

The first thing that I see is your fan is too deep into the shroud. There is a spec used for engine cooling called FOOS (Not Chip Foose), but it stands for Fan Out Of Shroud. It is the amount of the depth of the fan that overlaps with the fan shroud. For best performance you want the depth of the fan half way into the shroud and half way out of the shroud. 50% +/- 20% is the best. You can trim back the shroud or move the fan to correct.

Also how well "sealed" is the shroud. Can air get around the fan and/or shroud. You want the shroud to work as a nozzle to help pull and direct the air to flow THROUGH the radiator, not have any paths AROUND it.
Click to expand...

Thanks Kuda, this is the comment I was looking for. The fan is set in the shroud roughly a 1/2". I will cut the shroud back to reveal a third to a half of the fan blade. Around the circumference I have roughly 1/2" between the blade tips and shroud.

Andy
 
Kuda and Bob both hit it on the nose.
With the fan exposed it pulls a ton more air, and I'm pretty sure you are going to notice the difference with that alone.
However, it would work a lot better if you pull air through the whole cooling surface area of the radiator.
Check out the image below, as it shows the difference. (could you use 50% better cooling?)
Even though you have what you do on your car right now it still equates to the same thing as the fan and radiator on the left.
If yours was designed like the one on the right and your mechanical fan was about 1/3 or 1/2 out of the opening, you would never have a heat problem

A circle around the fan just limits the airflow to that circle only, so you are loosing literally about 1/3-1/2 of your cooling surface.
Most people don't realize that most of the air a fan blows comes from it's outer edges also so directing it straight back by being inside the shroud severely limits it's flow ability.
When the air comes off the blades you want it to be able to go everywhere it can so it pulls the most CFM.
 

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TrailBeast said:
Kuda and Bob both hit it on the nose.
With the fan exposed it pulls a ton more air, and I'm pretty sure you are going to notice the difference with that alone.
However, it would work a lot better if you pull air through the whole cooling surface area of the radiator.
Check out the image below, as it shows the difference. (could you use 50% better cooling?)
Even though you have what you do on your car right now it still equates to the same thing as the fan and radiator on the left.
If yours was designed like the one on the right and your mechanical fan was about 1/3 or 1/2 out of the opening, you would never have a heat problem

A circle around the fan just limits the airflow to that circle only, so you are loosing literally about 1/3-1/2 of your cooling surface.
Most people don't realize that most of the air a fan blows comes from it's outer edges also so directing it straight back by being inside the shroud severely limits it's flow ability.
When the air comes off the blades you want it to be able to go everywhere it can so it pulls the most CFM.
Click to expand...

Thanks for your response. My shroud pictures don't show it, but it does sit off of the radiator about an inch. The shroud Covers the entire cooling area. I'm probably losing some efficiency from the lack of gentle flowing angles, as shown in one of your pics.
Thanks,
Andy
 
IMHO the "flat" part of your shroud ought to be a lot deeper. Looks like it is probably less than an inch deep. Add an inch or so to the depth of that part, take some off of the round part to get the fan in the sweet spot, and you'll be whole lot cooler.
 
And remember, "New" does not mean a part is good. When I got me 68 back on the road my cap and thermostat were both new out of the box.

Both we're also bad straight out of the box.
 
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