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Hi guys, with temps getting Warner I was curious to get your thoughts on using a flex fan? Yes or no or do they work being so far away from the rad, SB 350 fairly stock with AC....thx

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On my SB 350 I removed the flex fan and my 72 now runs cooler with the stock style fan with the fan clutch plus my gas mileage improved although only slightly.

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I added a flex fan to my 71 350 no a/c in 1972 from a Z-28.

The original 4 blade was noisier, no over heating issues.

I bet the de-clutching fan pulls way more air at idle with those 7 blades! Cost more also.

Bruce

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My big block 402 was getting warm and the solution I found was to put a new clutch on the clutch fan.  I believe it was a heavy duty one, rather than standard.  There is also a supreme duty (if I remember the terms correctly), but read that it didn't cool all that much more than the heavy duty yet produced a lot more fan noise.  After replacing the clutch with the heavy duty one, I rarely ever get above 180 even on warm days.  So that could be an option if you're running a clutch style fan.

 

Ben

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Not a fan of flex fans (no pun intended). I had one on my 70 due to financial constraints at the time. It was an aluminum one and one day a blade broke off and luckily didn't take anything with it. If you think about it anything that flexes will be subject to fatigue. I have heard of the fiberglass ones doing it also. The only plus there is the blades are light enough to not usually do damage. Also testing has shown ( I think Engine Masters was the most recent ) that the clutch fan is the least amount of power loss over no fan at all. I have a clutch fan on mine right now that I am very happy with. David   

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Also wondering can you use that clutch fan without A/C?

John S

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Yes, I have a clutch fan like that on my 70 and it doesn't have the A/C parts on it anymore.  I'd like to get the A/C put back on and working again at some point, but the clutch fan works just fine without it.  Like I said, I did need to upgrade to the heavy duty clutch when I went to the big block though.  Keeps it nice and cool so far ever since then.

 

Ben

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Funny comment.. (I hope) about clutch or de-clutching fans.

 

What do they call the sound, made by this type of fan, when first starting the engine?

 

 

 

 

 

 

 

 

Morning sickness!

(as told to me by a Chevrolet engineer back int he 70's)

Bruce 

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Thanks I have a flex fan on and it functions fine, but as in a previous post I also worry about the durability and the possibility of a blade breaking off. Something like that never happens in your driveway at idle.

John S

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Ford had a recall on their flex fans in the 70's.

Rumor has it a mechanic was revving the engine after a tune up and the blade broke, cutting his neck and killing him.

One of my mechanic's at the Ford service dept. couldn't get a smooth idle on a customers car, I looked at it, shut off the engine and we found a missing blade or two causing an imbalance that felt like a rough idle.

I check mine, from a 72 Camaro, (not aftermarket junk) all the time.

Bruce

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My M.C. was overheating at stop lights. Called radiator shop and he gave me good advice. He said if it gets hot at the light, but cools off going down the road, you have a bad clutch on the fan. The usual test is to spin it and if it stops you think it is OK. It is not. He told me to pull it and if there is oil on the front of the clutch it is bad. It was. A new one made all the difference, and you could tell it with the hood open. I like the fan clutch over a flex fan, as I had to make a decision and chose to go with GM's design and it works.

 

Plus a chance to clean up the fan and paint it, which I had not done.

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Would it be ok to run a Heavy Duty fan clutch on a 350 small block. I have a new Advance Standard Duty on it now but doesn’t seem to be working. Tend to overheat in a drive thru or a parade or a long light.

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I had a very similar problem some years ago and turned out to be the Radiator was plugged.  Could keep it in control while motoring down the highway but when stopped or slowed, radiator temp would rise quickly.

I would check for a restricted flow in radiator first.

 

Doug 

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Well it’s a new brass and copper 3 row radiator. New cap, New water pump and thermostat, and hoses.New standard fan clutch.

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It only rises when in drive thru or a parade where not moving much.

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I also put a manual cutoff on the heater hose and once I cut it off it started to overheat.

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I would be suspect of the Thermostat then considering you had replaced your entire cooling system.  It sounds as the coolant isn't circulating enough to keep the motor in check at low RPM's.  I can't imagine how your blocking the heater hose would cause engine temperature to rise.  All the Hoses in their respective places?

I thought I had your answer with my 1st comment.  :doh:

 

Doug 

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I did change the fan clutch to the heavy duty version and it seems to be much harder to turn than the standard unit. If this doesn’t work I will check the radiator to see if there is a restriction. Thank you for your reply.

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