How Do U Tell If Clutch Fan Is Working Correctly?
 

How Do U Tell If The Clutch Fan Is Working Correctly?

Mine spins freely hot or cold.

I always thought that the fan would be highly resistive to spinning. With the engine off (duh), grab the blade and sling it over. If it rotates more than, oh, a third of a turn, it is questionable.

That kinda makes sense. In traffic the connection should be almost direct, allowing the fan to draw air thru. If the fluid connection is weak, the engine won't turn the blades.

That's how I go about it.
Another way to look, is when you kill the motor, the fan should stop almost as quickly and not spin.

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'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
E-mail longhornmail@yahoo.com
My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough?
Columbus Ohio

How to tell if a fan clutch is defective


Check for oil streaks (or dust collected on oil streaks) on the fan clutch. It's a sure sign that the internal fluid that provides the clutch action is leaking.
To check for a worn bearing, with the engine off, grasp the fan blade on either end and check for lateral movement. If there's more than 1/4" of side-to-side movement, the bearing is worn and the unit needs replacement.

In checking for proper fan clutch operation, first run the engine until operating temperature is reached. Next, with the engine off, give the fan blade a gentle spin. If it rotates more than twice the clutch is worn and needs replacing. If fan rotation is rough or noisy, or the fan fails to turn, the unit is worn out and needs replacement.

Article from Four Seasons.
2 turns is a bit excessive I think... 1 turn is a general rule of thumb. Or if you feel resistance while turning.

The tough part of checking these things is temperature. If you shut the vehicle off and the fan is engaged it will stop immediatly, if you stop it when the fan is coasting, it will freewheel for a few revolutions and give you the impression its bad.


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Pictures and more...
piston@zkast.com
'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
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Webmaster/Team owner
www.zkast.com
Garrett - Olathe, Kansas


[This message has been edited by Zkast (edited May 20, 2002).]

Zkast, that is all good if you have a thermostatic fan. Not all are.
Most just have oil in them, and as the RPM increases, the rotor and stator stop spinning at the same RPM. This is the type that comes in 99% of the V-8 GM vehicles.

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'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
E-mail longhornmail@yahoo.com
My name is Andy...not Randy...I'm in Ohio...Not Illinois...close enough?
Columbus Ohio

The info was from four seasons and doesnt differentiate between thermo or not. You still have to warm the engine to warm the oil in the fan clutch.. otherwise you will get a false test.

Most are fan clutches do have thermostat control built in. Older designs and special applications didnt but most do. If you find one that isnt, when it goes bad, replace it with a updated design... will save you some gas mileage.

------------------
Pictures and more...
piston@zkast.com
'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
------------------------------------------
Webmaster/Team owner
www.zkast.com
Garrett - Olathe, Kansas

Mine didn't work for a long time and I didn't know it. I checked all of the things mentioned above and found that my fan met all of criteria. Try this, with the engine cool start it up and listen to the fan as you raise the RPMs to 2500-3000. It should at first sound as if a prop plane is under the hood and then the sound should smooth out and become quiter. If the fan does not change tones, then it is the clutch on the fan. Give it a try. It worked for me.
Ben


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67 Fleetside Custom C-10
SBC 350 .030 9:1 comp.
Comp Cams Extreme Energy XE256H-10
Carter AFB 600
Edlebrock performer intake
Screw in rocker studs
Oversize valves
Scat 350 crank
Everything balanced within one gram.
Marine grade plywood bed(looks awsome)

Another good test http://67-72chevytrucks.com/board/ubbhtml/biggrin.gif

------------------
Pictures and more...
piston@zkast.com
'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
------------------------------------------
Webmaster/Team owner
www.zkast.com
Garrett - Olathe, Kansas