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(Which Fan Blade / Thermal Clutch Fan?) 72 SBO Cutlass

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(Which Fan Blade / Thermal Clutch Fan?) 72 SBO Cutlass

Old May 5th, 2019, 11:33 AM
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Question (Which Fan Blade / Thermal Clutch Fan?) 72 SBO Cutlass


I have a 72 Cutlass, with OEM fan shroud. Mark R built me a SBO stroked/bored to 434ci, over 500HP, near 600tq.

I want to get a new fan system, as the stock fixed fan is way too loud and inefficient. I want to get a thermal clutch fan and a fan for it that will fit perfectly in the stock fan shroud, but am not sure what size fan that is and/or which thermal clutch and fan to replace it all with.

Any insights?
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Old May 6th, 2019, 02:49 PM
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Measure the inside diameter of the fan shroud and look for a GM 7 blade clutch fan. People are asking way too much for them already unless you know a yard with old cars in it. Any fan will do that fits. Cadillac, Pontiac, Olds etc. Then get a Hayden heavy duty fan clutch from the parts store. The air conditioning model. About $60. That setup will work as well as an electric fan setup and will be dead reliable. Do you have a four core radiator or an aluminum one? Either one should do the job. A brass 4 core gets the job done on my 455 GTO and a $150 aluminum radiator from Summit gets the job done on my 500 Cadillac. Both have shrouds.
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Old May 7th, 2019, 03:14 AM
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What he said. I got my 7 blade fan from a mid 70s square body Chevy truck. With my aluminum Be cool radiator it never runs more than about 210-215, idling, in traffic, with the A/C going. As for mechanical fans taking power to run, the car ruins the same at the track with the fan installed or removed. Unless the engine is hot enough to engage the thermal clutch, the fan is just along for the ride. You can definitely hear the roar of the fan when it does engage.
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Old May 7th, 2019, 06:38 AM
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I can't hear my 4 blade factory fan and it works quite well. As said a 7 blade fan and a heavy duty clutch or leave what you have. Maybe the shroud makes it noisy, I don't have one on my 70S.
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Old May 7th, 2019, 11:24 AM
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I used a Hayden standard duty thermal on my 442 and it worked well. Amazon had a good price on it.

This link gives some good info

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Old May 7th, 2019, 06:27 PM
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Hayden specifically recommends NOT using a "Heavy Duty" or "Severe Duty" fan clutch with any fan having typical automotive-style pitch to the blades. Without a fan that has serious blade pitch, the clutch will never disengage.

A standard-duty thermostatic clutch (NOT a centrifugal clutch) is all you need. The OEM recommendation is probably fine. I had to get creative on my Toronado because--apparently--the OEM clutch length is no longer available. The fan should be between 1/3--1/2 in the shroud, 2/3--1/2 out of the shroud.

Centrifugal clutches are for people who won't pay the money for a product that performs properly. They're junk.

Last edited by Schurkey; May 7th, 2019 at 06:29 PM.
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