#21  
Old 06-20-2021, 11:47 AM
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My brother's 461ci powered 1974 GTO struggled for years with running too hot. It was basically impossible to keep it under 190F, and it would be over 200F and climbing anytime you got stuck in traffic. We installed an Edelbrock high-flow aluminum water pump, Cold Case aluminum radiator, and ditched the ugly clutchless flex-fan for a stock fan with heavy-duty clutch from Ames. Now it cruises at 170F and pretty much never gets above 180F in traffic during hot and humid Michigan summers. He used to have major problems with hot starting, and now all those issues are gone. Big transformation.

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Last edited by ZeGermanHam; 06-20-2021 at 11:54 AM.
  #22  
Old 06-20-2021, 12:03 PM
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Another reason to always look for a car with AC, they have a heavy duty cooling system. The heater is even better.

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  #23  
Old 06-20-2021, 12:12 PM
PontiacJim1959 PontiacJim1959 is offline
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Quote:
Originally Posted by Fullback66 View Post
Why is this fan clutch better? Is it because it spins faster?
I do not have A/C. This has been a huge help. Thanks to all the guys who replied.
Cross my fingers.
Thanks
FB66
No the fan does not spin faster. I am going to say it works better because it is due in part that the factory fan that is used with the clutch has more blades and the pitch is more aggressive so it pulls more air at lower speeds.

As the RPM's increase that is when the clutch mechanism comes into play. The clutch has fluid inside it that allows the fan to slip once it reaches a certain RPM where the movement of the car through the air forces enough air through the radiator to do its job. Thus, you do not lose HP needed to continue to rotate the fan blades as engine RPM goes up as you would with a solid non-clutched fan.

This is the same principal as a flex fan. More blades at a greater pitch, but they flatten out as the RPM's increase and no longer rob power needed to rotate the fan if they did not flatten out. Once your engine gets down into the lower RPM's/slow driving, the flex fan returns to its greater pitch angle just as the clutch fan mechanism begins to "grab" the fan at lower RPM's and does not slip as it had at the higher RPM's - think of the clutch fan just like a torque converter, except in reverse, the torque converter slips until enough RPM's cause the fluid to move the stator fins that engage/lock up the transmission and the car moves forward. The clutch fan engages/operates the minute the engine is fired up and then the internal fluid slips when the engine RPM's get higher. Then fan is still rotating, but it no longer continues to speed up with higher engine RPM's.

  #24  
Old 06-20-2021, 12:25 PM
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And would need to run the math but a fan in air does not increase CFM as RPM, there is a certain speed after which the blades interfere with each other and flow goes down. Eventually you reach something called "choked flow". A clutch fan is designed to reach that max flow speed and go no faster.

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  #25  
Old 06-21-2021, 03:27 AM
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To go a little deeper into the operating characteristics of the clutch fan we can start out with a quote right off Hayden's website:

What is the difference between a standard, heavy and severe duty fan clutch?

Answer: Each fan clutch type is designed to simulate the performance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should be applied only on the vehicle for which they are cataloged. Use of the incorrect fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.

• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface.

• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's.

• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy
.

Their heavy duty thermal clutch characteristics were changed by Hayden a few years ago. Was 70-80% but now rated the same as the severe duty. I'd be okay with either one but the severe duty is much easier to locate and still seems to engage stronger.

Most important thing about a clutch fan is the viscous fluid and (as mentioned above) the ability to freewheel at speeds above about 4,600 RPM. The fluid normally hooks up the impellers but at the specified RPM centrifugal force pulls the fluid towards the perimeter of the clutch and keeps the clutch and fan from reaching any higher RPM and the fan simply stays at about 4,600 RPM while the engine winds higher. Also remember the over-driven water pump and fan reach speeds in excess of engine RPM.. The fan assemblies would become lethal weapons if allowed to RPM with the engine when you add in the 14% overdrive. I normally shift at 6,300 RPM and without the slippage the 19.5" fan would be turning 7,200 RPM.

Next thing is how strongly the different clutches engage, and the severe duty simply has a much higher lockup ratio. A worn out clutch fan might be down to 30% engagement or even less, and that's why it's best to replace it with a new unit.

Just like we add headers, aluminum heads, better intake manifolds and such, going above a stock fan clutch just makes sense.

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  #26  
Old 06-21-2021, 08:23 AM
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200-205 with stoplights and 85degree temp is perfectly normal especially if it went back down to 190 once you were moving again. For us, 85 is a nice winter day, but with low humidity. I have always cross checked my gauges with the infrared thermometer, and seldomly do any of them read as low as it does.

  #27  
Old 06-21-2021, 03:47 PM
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Quote:
Originally Posted by lust4speed View Post
To go a little deeper into the operating characteristics of the clutch fan we can start out with a quote right off Hayden's website:

What is the difference between a standard, heavy and severe duty fan clutch?

Answer: Each fan clutch type is designed to simulate the performance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should be applied only on the vehicle for which they are cataloged. Use of the incorrect fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.

• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface.

• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's.

• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy
.

Their heavy duty thermal clutch characteristics were changed by Hayden a few years ago. Was 70-80% but now rated the same as the severe duty. I'd be okay with either one but the severe duty is much easier to locate and still seems to engage stronger.

Most important thing about a clutch fan is the viscous fluid and (as mentioned above) the ability to freewheel at speeds above about 4,600 RPM. The fluid normally hooks up the impellers but at the specified RPM centrifugal force pulls the fluid towards the perimeter of the clutch and keeps the clutch and fan from reaching any higher RPM and the fan simply stays at about 4,600 RPM while the engine winds higher. Also remember the over-driven water pump and fan reach speeds in excess of engine RPM.. The fan assemblies would become lethal weapons if allowed to RPM with the engine when you add in the 14% overdrive. I normally shift at 6,300 RPM and without the slippage the 19.5" fan would be turning 7,200 RPM.

Next thing is how strongly the different clutches engage, and the severe duty simply has a much higher lockup ratio. A worn out clutch fan might be down to 30% engagement or even less, and that's why it's best to replace it with a new unit.

Just like we add headers, aluminum heads, better intake manifolds and such, going above a stock fan clutch just makes sense.

So, are you saying you would go up on the clutch? Or, go stock? Your last sentence got me a little confused.

Thanks,
FB66

  #28  
Old 07-30-2021, 07:39 AM
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Talking with a guy at our weekly cruise night. He told me I should get a spacer to get the fan closer to the radiator.
Has anyone done this? Does it work?
Let me know.
Thanks
FB66
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  #29  
Old 07-30-2021, 06:22 PM
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I always upgrade to the severe duty fan. Only had one club member hate the SD fan because of the additional fan noise under load. Funny thing is he lives in Palm Springs and the fan was simply doing what it needed to do. I haven't stepped down to the HD but the specs would indicate it would be a suitable choice in moderate temperature areas.

Most spacers are designed for a standard or flex fan and not to be used with a clutch fan. The spacer is meant to position the flex fan blades about where the clutch fan would locate them. Using a spacer with the clutch is going to amplify any minor imbalance in the fan blades and lead to a possible bearing failure in the water pump. Many years ago I had a bearing come loose in a new Cardone water pump and it allowed the fan to tilt and chew a hole in the radiator.

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  #30  
Old 08-01-2021, 05:58 PM
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Thanks lust5speed.
FB66

  #31  
Old 02-13-2022, 03:27 PM
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Quote:
Originally Posted by ZeGermanHam View Post
My brother's 461ci powered 1974 GTO struggled for years with running too hot. It was basically impossible to keep it under 190F, and it would be over 200F and climbing anytime you got stuck in traffic. We installed an Edelbrock high-flow aluminum water pump, Cold Case aluminum radiator, and ditched the ugly clutchless flex-fan for a stock fan with heavy-duty clutch from Ames. Now it cruises at 170F and pretty much never gets above 180F in traffic during hot and humid Michigan summers. He used to have major problems with hot starting, and now all those issues are gone. Big transformation.
What Thermostat are u running 180? 160? I ran Hot until I finally got a Griffin Alum
Hi Performance 1 1/4 two row unit similar 461 on my 66

  #32  
Old 03-27-2022, 04:34 PM
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Severe Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged.
Turns the fan 20-30% of the shaft speed when
disengaged.
Used with deeper pitch fans. (2 -1/2” of pitch).
Land and groove design with up to 72 Sq. In.
of working area.
Larger working surface provides cooler running
and longer life expectancy.
Thicker body and deep finned faceplate dissipate more heat.
Can be used in place of many
heavy-duty clutches.

Are stock fans pitch 2-1/2 inches?????

  #33  
Old 03-29-2022, 09:44 AM
66sprint6 66sprint6 is offline
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Does the severe duty clutch have a larger depth than the heavy duty? I was looking online and it seems like it would push the fan further into the shroud on my '67. I understand that the fan/shroud relationship is crucial.

  #34  
Old 03-29-2022, 10:08 AM
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Look through their catalogue. I used a severe duty clutch on my '64 GTO. I think it's for an Olds Toronado or something. Just look for the correct pilot diameter, bolt pattern, etc. Find one that's the right length for your car.

https://www.haydenauto.com/media/558...utch-pages.pdf

  #35  
Old 03-29-2022, 04:18 PM
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Quote:
Originally Posted by 66sprint6 View Post
Does the severe duty clutch have a larger depth than the heavy duty? I was looking online and it seems like it would push the fan further into the shroud on my '67. I understand that the fan/shroud relationship is crucial.
Yes and no. The fan itself bolts up the same distance from the water pump shaft flange. The fan bolts up to the rear of the aluminum clutch and only the thicker aluminum clutch protrudes further forward. The flan blades are still the same distance from the radiator with the standard, heavy duty, or severe duty clutches.

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Last edited by lust4speed; 03-29-2022 at 04:25 PM.
  #36  
Old 03-30-2022, 08:17 AM
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Are stock Fan pitch 2-1/2"?

  #37  
Old 03-30-2022, 09:22 AM
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202-205 Running down the Highway in the New Hampshire Summah…65 Mph…I get off the exit..the temp drops to 195

  #38  
Old 03-30-2022, 01:51 PM
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Quote:
Originally Posted by Fullback66 View Post
Are stock Fan pitch 2-1/2"?
I keep forgetting to pull a 19.5 fan off the shelf to measure depth. Now the strange thing about the manufacturer stating a 2-1/2" pitch is it is ambiguous - "pitch" should be 1 in 1, 1 in 2 or some other number that references drop to distance. I don't think we can us a 2.5:1 pitch because the blades would be nearly horizontal to the water pump shaft centerline, and many of the older trucks that the SD came on had similar fans to the Pontiac AC fan. Maybe we can figure the company wants a total drop of 2.5" from front to rear, and the Pontiac AC fan has that or comes really close.

I can tell you that I have successfully run the severe duty on my original HO 18" fan and many 19.5" fans. Currently have a SD clutch on my GTO, the 2+2, the wagon, and the Bonneville 2DR HT -- and that isn't counting our club cars that run that fan clutch.

Just as well put in an update here on the latest install on the Catalina wagon. It has a new (and still tight) 496ci stroker. It came off the run stand and into the car last month and we are getting some break-in miles on it. Autometer temp gauge was showing between 195 and 200 degrees, but it wouldn't go over that. Figured that's where Hayden had the fan clutch set so I did the fan tweak bending the tip of the coil spring a little farther than normal but figured I test it there. Since then we haven't been able to get the car hotter than the thermostat 160°. Went a little farther than normal on the bend, but summer is coming so will leave it there.

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  #39  
Old 03-30-2022, 02:25 PM
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Thanks for the feedback. Lust4speed

  #40  
Old 06-16-2022, 09:27 AM
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One more question.
I installed the Hayden 2797 severe duty clutch to my fan.
I do get a little squeal when I rev up the RPMs . Not all the time.
Question:
Is this a belt issue? or does the clutch squeal?
Thanks
FB66

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