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*72longbed* · 06-22-2004, 12:17 AM

OK, here it is.
1. Which one cools better, a clutch fan thats 'Thermally' controlled or a clutch fan thats 'RPM' controlled??

2. Which one eats less horsepower??

3. Can you use a clutch fan from a big block on a small block??

4. Is there a difference in A/C clutch fans vs. non-A/C clutch fans??

Please give your best answers, the member who gets them all right wins a prize!!

**67 cst swb** · 06-22-2004, 01:51 AM

answer #1) Thermostatically Controlled cool better... it's controlled by a thermostat to clutch the fan more or less depending on Temp.

answer #2) a Thermo probably is less power robbing due to more free spinning after cooling down therefor the thermostat frees up clutch, but probably also too little to notice a difference in HorsePower. It takes approx. 20-25HP to notice a difference in the seat of your pants feel...

answer #3) B/B to S/B... I'm sure they might interchange as far as bolting up goes, but as far as application goes a B/B requires more cooling so, a tighter clutching type is required

answer #4) (see answer #3) A/C to non A/C... an A/C vehicle requires more cooling, so by the application, for example, a 72 350 1/2 ton truck takes part# 1234 w/o A/C and a part# 4321 for w/ A/C...

DO I WIN...?

68C15 · 06-22-2004, 07:32 AM

#1 electric cools better due to being placed closer to heat exchanger.

#2 electric consumes less torque (horse power is a mathematical derivative of torque)

#3 sure, if you like the sound of crop dusters under your hood

#4 translates to thermal-centrifugal question

can you tell I prefer electric fans? why do you think car manufacturers use them? any good parts store (sturdevants) will sell you a fan switch to thread into either the intake or cylinder head. intake runs about 15 deg. cooler.

68C15 · 06-22-2004, 07:36 AM

BTW Bryan, did you get those #s from the book? ha-ha
do you know the #s for these switches as I lost the box mine came in.
Todd
TS46 rings a bell for some reason

67chevemall · 06-22-2004, 09:26 AM

I messed with ever fan I could find Then gave up
and purchased a Summit 18" electric!
Works so sweet I love it!
I have dims on the sheet metal brackets I made if interested!
Cheers

*72longbed* · 06-22-2004, 10:31 AM

This is good stuff so far, but I think there might be some confusion.

I am not comparing 'electric' fans here at all. When I ask about the two types of clutch fans, they are not electrically activated.

RPM vs. Thermal is two different types of clutches that were put on GM vehicles.

So..........., who has the knowledge of these different clutch fans to be able to offer an educated opinion??

72longbed

67chevemall · 06-22-2004, 10:36 AM

Cool Man I got it now!
Speed of the engine or heat to engage fan!
Good Question

Vince M · 06-22-2004, 06:11 PM

The "thermal" clutch has a silicone based fluid in it that gets thicker as it gets hotter which drives the turbine inside it more as the temp goes up. I've never seen the "RPM" units but they must have some sort of centrifugal weight that would drive it as RPM goes up.

Personally I vote for the "thermal" unit. It only uses horsepower when it needs it.

jimfulco · 06-22-2004, 10:00 PM

The non-thermal-clutch viscous-drive fans sound like an airplane all the time. The thermal-clutch fans only sound like one when the radiator gets over a certain temperature.

68C15 · 06-22-2004, 10:30 PM

the main problem some ppl have with the thermal units is if there is too much gap between the rad. & clutch it does not come on soon enough. same thing with not having full shroud.
I personally cannot think of a reason to use the centrifugal type. by the time they engage you are going fast enough to have airflow without it.
what it comes down to in my opinion is either run electric or thermal with fan 1/2 way into shroud.
hopes this helps clear things up a little

06-22-2004, 09:26 AM	#5
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	I messed with ever fan I could find Then gave up and purchased a Summit 18" electric! Works so sweet I love it! I have dims on the sheet metal brackets I made if interested! Cheers __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

06-22-2004, 10:36 AM	#7
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Cool Man I got it now! Speed of the engine or heat to engage fan! Good Question __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

06-22-2004, 06:11 PM	#8
Vince M Senior Member Join Date: Apr 2000 Location: Orlando, FL Posts: 1,076	The "thermal" clutch has a silicone based fluid in it that gets thicker as it gets hotter which drives the turbine inside it more as the temp goes up. I've never seen the "RPM" units but they must have some sort of centrifugal weight that would drive it as RPM goes up. Personally I vote for the "thermal" unit. It only uses horsepower when it needs it. __________________ ............................................................ 68 Chevy CST SWB w/LS1, carb & 700r4. Golden Anniversary clone with a few improvements.

06-22-2004, 10:30 PM	#10
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	the main problem some ppl have with the thermal units is if there is too much gap between the rad. & clutch it does not come on soon enough. same thing with not having full shroud. I personally cannot think of a reason to use the centrifugal type. by the time they engage you are going fast enough to have airflow without it. what it comes down to in my opinion is either run electric or thermal with fan 1/2 way into shroud. hopes this helps clear things up a little __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

06-22-2004, 12:17 AM	#1
72longbed Account Suspended Join Date: Jun 2003 Location: PA Posts: 1,411	Who Knows The Answers?? OK, here it is. 1. Which one cools better, a clutch fan thats 'Thermally' controlled or a clutch fan thats 'RPM' controlled?? 2. Which one eats less horsepower?? 3. Can you use a clutch fan from a big block on a small block?? 4. Is there a difference in A/C clutch fans vs. non-A/C clutch fans?? Please give your best answers, the member who gets them all right wins a prize!! Last edited by 72longbed; 06-22-2004 at 12:21 AM.

06-22-2004, 01:51 AM	#2
67 cst swb Senior Member Join Date: Nov 2001 Location: Rapid City, SD Posts: 2,281	Ok,...I'll try answer #1) Thermostatically Controlled cool better... it's controlled by a thermostat to clutch the fan more or less depending on Temp. answer #2) a Thermo probably is less power robbing due to more free spinning after cooling down therefor the thermostat frees up clutch, but probably also too little to notice a difference in HorsePower. It takes approx. 20-25HP to notice a difference in the seat of your pants feel... answer #3) B/B to S/B... I'm sure they might interchange as far as bolting up goes, but as far as application goes a B/B requires more cooling so, a tighter clutching type is required answer #4) (see answer #3) A/C to non A/C... an A/C vehicle requires more cooling, so by the application, for example, a 72 350 1/2 ton truck takes part# 1234 w/o A/C and a part# 4321 for w/ A/C... DO I WIN...? __________________ My Trucks: 1967 Chevrolet Short Wide Box 327 TH350 9" w/3.90 gears paint will be White - Current Project 1967 Chevrolet Custom LWB 283 TH400 3.73 Posi, no-AC, no-PS, no-PB, bench-seat, small-window - mostly orig driver 1967 Chevrolet CST LWB originally a 327 TH400 3.73 Posi AC PS PB, had Buddy Buckets, Small Window - parts truck 1967 Chevrolet CST LWB, 283 MT 3.73 had Buddy Buckets, Panoramic Window - parts truck 2001 Chevrolet 3500 2WD Crew Cab Dually 8.1L Allison White Last edited by 67 cst swb; 06-22-2004 at 02:00 AM.

06-22-2004, 07:32 AM	#3
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	#1 electric cools better due to being placed closer to heat exchanger. #2 electric consumes less torque (horse power is a mathematical derivative of torque) #3 sure, if you like the sound of crop dusters under your hood #4 translates to thermal-centrifugal question can you tell I prefer electric fans? why do you think car manufacturers use them? any good parts store (sturdevants) will sell you a fan switch to thread into either the intake or cylinder head. intake runs about 15 deg. cooler. __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

06-22-2004, 07:36 AM	#4
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	BTW Bryan, did you get those #s from the book? ha-ha do you know the #s for these switches as I lost the box mine came in. Todd TS46 rings a bell for some reason __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

06-22-2004, 10:31 AM	#6
72longbed Account Suspended Join Date: Jun 2003 Location: PA Posts: 1,411	This is good stuff so far, but I think there might be some confusion. I am not comparing 'electric' fans here at all. When I ask about the two types of clutch fans, they are not electrically activated. RPM vs. Thermal is two different types of clutches that were put on GM vehicles. So..........., who has the knowledge of these different clutch fans to be able to offer an educated opinion?? 72longbed

06-22-2004, 10:00 PM	#9
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	The non-thermal-clutch viscous-drive fans sound like an airplane all the time. The thermal-clutch fans only sound like one when the radiator gets over a certain temperature.



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