Thermal vs. Non-Thermal Fan Clutch - Chevelle Tech
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post #1 of 33 (permalink) Old Jun 22nd, 03, 10:55 PM Thread Starter
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Ron
 
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Hi guys:

Would like to know the difference between the two types of fan clutches, and which is considered better for a performance street-driven car (BBC if it matters) with a 7 blade fan?

All comments are appreciated.

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post #2 of 33 (permalink) Old Jun 23rd, 03, 2:18 AM
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Thermal clutch: The rate at which the fan spins is not the same as the water pump's shaft. The speed of the fan is directly proportional to the heat of the motor & the water pump's shaft. Hence the "clutch" part. Laymens terms: It slips and doesn't spin as fast while the motor is cold... then spins more as the motor heats up.

Non-thermal clutch: speed is directly coupled to the water pump's shaft.

The latter is usually cheaper and will not wear out of time. The thermal will (like any slipping system) begin to slip more over time and you loose efficiency and cooling ability.

however, living in a cold place (get's pretty cold up there 'ey?) the thermal-clutch fan is preffered, as it allows your motor to come to operating temperatures sooner.

Besides, when they built these cars some brainiac thought up this thermal clutch for a reason. [img]smile.gif[/img]

That'll be $10 (american) [img]graemlins/thumbsup.gif[/img]

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post #3 of 33 (permalink) Old Jun 23rd, 03, 8:28 AM
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While I dont dispute anything Mike says, I chose the simpler, CHEAPER mechanical clutch. Works mint. Least it doesnt spin at 7000 rpms anymore!

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post #4 of 33 (permalink) Old Jun 23rd, 03, 8:36 AM
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post #5 of 33 (permalink) Old Jun 23rd, 03, 9:21 AM
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Just a quick correction to Mikes nonthermal definetion... It too slips or it wouldn't be any different than the mechanical fan Gene uses. The nonthermal is tighter or spins closer to engine rpm at lower rpms (when it is needed the most for cooling) and then as rpm increases it loosens up (slips more) and spins at a lower rpm than the engine.
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post #6 of 33 (permalink) Old Jun 23rd, 03, 1:09 PM Thread Starter
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Thanks guys, that was my guess.

It sure is cold up here Mike, I just took the v-plow off the velle for the summer!

Is there a reason besides cost that leads you to the non-thermal (because they will spin at high rpms?)?

How do they work? I guess the non-thermal is a centripal weight set-up?

Does anyone have a GM part# for a the non-thermal type?
TIA
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post #7 of 33 (permalink) Old Jun 23rd, 03, 7:22 PM
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Hey Bow_Tied, Is Eastown Chevrolet still around,My 68 SS came from London Ontario..
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post #8 of 33 (permalink) Old Jun 23rd, 03, 7:31 PM Thread Starter
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Quote:
Originally posted by Daves68:
Hey Bow_Tied, Is Eastown Chevrolet still around,My 68 SS came from London Ontario..
Sort of - It is now called MacMaster Chev/Olds, 1470 Dunda St., (519)455-6200. I have found the parts guys there nice, but quite useless if the computer cannot tell them the answer with 30 seconds. No time for the little guy I guess.

Have you purchased your GM Canada documentation/build info?
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post #9 of 33 (permalink) Old Jun 23rd, 03, 11:02 PM
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I did manage to screw that up didn't I.
Once you go electric, you forget all of those "details".

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post #10 of 33 (permalink) Old Jun 23rd, 03, 11:04 PM
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Quote:
Originally posted by Bow_Tied:
Thanks guys, that was my guess.

It sure is cold up here Mike, I just took the v-plow off the velle for the summer!

Is there a reason besides cost that leads you to the non-thermal (because they will spin at high rpms?)?

How do they work? I guess the non-thermal is a centripal weight set-up?

Does anyone have a GM part# for a the non-thermal type?
TIA
Here's a good thread on fans on the camaro site...

http://www.camaros.net/cgi-bin/forum...;f=19;t=000064

I'm using a nonthremal from summit that the fan and clutch were very reasonable. I post number and cost in the link...
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post #11 of 33 (permalink) Old Jun 23rd, 03, 11:22 PM Thread Starter
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Thank-you Dennis, that was an informative thread - I had no idea the HP differences between mechancial and electric!
Ron
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post #12 of 33 (permalink) Old Jun 24th, 03, 4:31 PM
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Thanks Bow_Tied, The GM info from Canada came with the car when I bought it, Nice little packet of info...
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post #13 of 33 (permalink) Old Jun 24th, 03, 7:37 PM
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A quote from a 1970 Pontiac engineering brochure: "Fans. They cool. They also eat horsepower. Conventional fans slurp up 20-24 horses @ 6000 fan rpm. Flex fans, about 5 or 6. And a clutch fan, about 4 or 5 horses. Take your choice. Why the difference? The flex fan blades flatten out at high rpm. Less resistance. Less drain. The clutch fan is thermostatically controlled. Cold, it runs no faster than 1000 rpm. Hot, it engages and picks up to 1800 rpm. All because of a little clutch."

What I can add is that flex fans flex, but that leads eventually to fatigue of the blades and some nasty shrapnel will result. They were recalled a few years back for that very reason.
Clutch fans are great. More efficient for warm-ups, move lots of air at low engine rpm yet they don't have the fan roar at high rpm. If they wear out they can either fail to uncouple completely, or they can do just the opposite.
Electric fans? Sounds like a plan. Just remember that your alternator will add it's own drag to power the electric fan. Energy is neither created or destroyed, it is converted. Hopefully little is lost along the way.

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post #14 of 33 (permalink) Old Jan 12th, 12, 11:30 PM
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Re: Thermal vs. Non-Thermal Fan Clutch

For a place like Texas where it never gets colder than 30 degrees (while I'm driving anyway) and most of the time it's HOT weather!
would I go with thermal non-thermal?

Thermal, that,sucker would spin when I need it.
Non thermal, doesn't where out as fast.
Thermal keeps my motor running cooler as I might need it more here in Texas.

I'm thinking thermal.

any more food for though? Agree? Disagree?

Mark

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post #15 of 33 (permalink) Old Jan 13th, 12, 12:45 AM
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Re: Thermal vs. Non-Thermal Fan Clutch

Direct info from the manufacturer:

http://www.haydenauto.com/Featured%2...s/Content.aspx

Quote:
Non-Thermal Fan Clutch
  • Low cost alternative for some standard thermal clutches.
  • Always engaged, less fuel savings than a thermal clutch.
  • Spins at about 30-60% of the water pump speed.
  • Shorter life expectancy.
  • Cannot replace a heavy-duty clutch.
  • Identified by the smooth, steel faceplate, (without a thermal spring assembly), on the front.
Quote:
Thermal Fan Clutch
  • Varies the fan speed with temperature of the air behind the radiator.
  • Engaged (high speed) operation provides maximum cooling.
  • Disengaged (low speed) operation provides fuel savings and noise reduction.
  • Greater life expectancy than a non-thermal clutch.
  • Briefly engaged at cold start-up.
  • Engages at about 170 radiator air temperature, (about 30 lower than coolant temperature).
There is also a three-page tutorial. Page 1:
http://www.haydenauto.com/Fan%20Clut...1/Content.aspx

Far as I'm concerned, non-thermal fan clutches are junk for people who refuse to spend the money for a real fan clutch.

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