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Discussion Starter #1
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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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.


That'll be $10 (american)
 

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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! :eek:
 

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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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Discussion Starter #6
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! :eek:

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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Discussion Starter #8
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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I did manage to screw that up didn't I.
Once you go electric, you forget all of those "details". :D
 

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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! :eek:

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/ultimatebb.cgi?ubb=get_topic;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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Discussion Starter #11
Thank-you Dennis, that was an informative thread - I had no idea the HP differences between mechancial and electric!
Ron
 

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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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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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Direct info from the manufacturer:

http://www.haydenauto.com/Featured Products-Fan Clutches and Fan Blades/Content.aspx

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.
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 Clutch Tutorial-Part 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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Mark I see you are here also. Buy the Hayden. When you look in the book look for one that specifies HD or Police Duty. In Austin heat you might get away with std. duty but why chance it for a small amount of money. You might find more info in the Heating/Cooling section.

Probably Hayden #2797
 

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Thanks John! oh i posted in the wrong area! :eek:
 

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There is no wrong area around here. Only questions that need answers.
 

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Non thermal fan clutch does the job BUT it runs all the time wasting fuel ,makes more noise,uses same amount of HP to run all the time vs therm fan clutch that only needs most power to run when motor is hot fully locking up a therm fan ,also pulls more dirt into engine compartment too.

Thermal fan clutch makes less noise on avg because its not always locked up and is only locked up for more fan speed/additional cooling when motor/cooling system heats up enough.

Thermal fan cutch pulls in less dirt into engine bay bacuase again its not always locked upand is only locked up for more fan speed/additional cooling when motor/cooling system heats up enough.

Thermal fan clutch uses less fuel for same reasons stated above.

Uses less power to run when motor /cooling system isnt hot enough to fully lock up fan clutch.

This is why i prefer & rec running only high quality Hayden std duty or HD (for even more cooling) thermal fan cluches on sbc/bbc street perf apps along with GM clutch fans used on their HD cooling or AC options.

Also found autozones std flow 15356 stat with bypass hole reduced overall stablized cooling system temps by 10-15 deg on avg (at time recued by 20+ deg) in 85-90+ deg temps vs using one of the hi perf hi flow stats on the market these days that often dont open fully/properly reducing coolant flow resulting in considerably hotter cooling system/motor temps.

But more times then not i use Hayden HD therm fan clutches for street perf apps esp for BBC apps with great results every time.

There are other therm fan clutches on the market today that dont work well but i have have had good/consistant results using hayden thermal fan clutches whyich is why i use & rec them too.

But i tend to stay away from Severe duty therm fan clutches,not that they dont work well because Hayden sever duty therm fan clutches work very well . But it's because some thermal sever duty fan clutches lock up earlier at lower temp & all severe duty therm fan clutches lock up tighter for considerably more fan rpm then a HD therm fan clutch does .

So with that said the severe duty therm fan clutch can end up having the same type negative issues to some people (not all) that the non thermal fan clutch has too like being more noisey,using more fuel,take more power to run,sucking more dirt into engine bay,etc.

If you have a real cooling issue a sever duty therm fan clutch will out cool a non thermal or HD therm fan clutch by a considerable amount posswibly fixing the issue if you don't mind the negative aspects of running a sever duty fan clutch as i mentioned above.

Just my 1st hand exp / $.02 on that one.

Scott
 
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