Clutch fan - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gman · 03-18-2003, 03:22 PM

Can someone explain how to tell whether a clutch fan is working correctly? Seems like it should not move at certain times but I can't remember when exactly. Should the fan rotate when the motor is completely COLD? What tests can be performed to check that its functioning correctly? How do these things work exactly? Thanks everyone.

JimKshortstep4x4 · 03-18-2003, 07:43 PM

Most of the clutch fans work because they have a fluid in them that gets more viscous as the temperature goes up, so the fan will be driven more. There are a couple of checks that you can make on your fan. Usually an old fan is not good. Check for looseness by shaking and try spinning it by hand, if it coasts it is bad. They go bad gradually, so if your engine overheats while idling, there is a good chance that the clutch is bad.

Jim

Mike C · 03-18-2003, 11:18 PM

There are two types. Thermostatically controlled and non-tstat controlled. The tstat one has a wound spring on the nose, kind of like a choke springs. When the air gets hot enough through the radiator, the spring engages the clutch and the fan sounds like a jet engine!

The non-tstat just freewheels to some degree as RPM goes up. You can get a tstat one from the parts store for about $30. Or about $150 from GM

68speedalert · 03-19-2003, 01:15 AM

You should be ables to turn the blade with the engine off and cold but have some resistance. I usually check it's operation with engine running.
It's harder to tell on these older trucks. On newer models, with the factory set-up, on a cold engine(fast idleling), you will hear the fan ROAR loudly. After running for 2-3 minutes (longer if colder) the clutch will begin to cycle in & out. After a short time it will cycle out completely and the roar will be gone.

If the fan never roars when cold, my guess is it's bad.

Checking if it comes in at the right temp is rather tricky. According to the book you're supposed to measure the temp of the air flowing through the rad in front of the clutch. If the temp gets too high before it cycles in, it's bad. Usually when it gets really hot outside and you've been running hard, watch the fan. If it looks like it is turning a lot slower than the engine, it might be bad. Sometimes they are so bad you can grab the fan blade and stop it while the engine is idleling. DO NOT TRY THIS!!!!!!!!!!!!!!!!!

Do Not buy the non-stat clutches. Also if you buy too much of a "heavy duty" clutch, your fan blades won't heat up the fluid in the stat enough and the clutch will never cycle out. Then no one will hear your daul exhaust because all they hear is the fan roaring.

Steve

Lightspeed · 03-19-2003, 01:50 AM

is it hard to switch from a clutch type fan to just a regular fan?

68speedalert · 03-20-2003, 02:38 PM

By regular fan do you mean one without any clutch?

Steve

HotRod929 · 03-20-2003, 03:35 PM

Could you swap from the stock 16" clutch fan to a 16" electric fan and still have adequite cooling? Thanks

HotRod

03-18-2003, 03:22 PM	#1
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	Clutch fan Can someone explain how to tell whether a clutch fan is working correctly? Seems like it should not move at certain times but I can't remember when exactly. Should the fan rotate when the motor is completely COLD? What tests can be performed to check that its functioning correctly? How do these things work exactly? Thanks everyone. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

03-18-2003, 07:43 PM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Most of the clutch fans work because they have a fluid in them that gets more viscous as the temperature goes up, so the fan will be driven more. There are a couple of checks that you can make on your fan. Usually an old fan is not good. Check for looseness by shaking and try spinning it by hand, if it coasts it is bad. They go bad gradually, so if your engine overheats while idling, there is a good chance that the clutch is bad. Jim Last edited by JimKshortstep4x4; 03-18-2003 at 07:45 PM.

03-18-2003, 11:18 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	There are two types. Thermostatically controlled and non-tstat controlled. The tstat one has a wound spring on the nose, kind of like a choke springs. When the air gets hot enough through the radiator, the spring engages the clutch and the fan sounds like a jet engine! The non-tstat just freewheels to some degree as RPM goes up. You can get a tstat one from the parts store for about $30. Or about $150 from GM __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

03-19-2003, 01:15 AM	#4
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	You should be ables to turn the blade with the engine off and cold but have some resistance. I usually check it's operation with engine running. It's harder to tell on these older trucks. On newer models, with the factory set-up, on a cold engine(fast idleling), you will hear the fan ROAR loudly. After running for 2-3 minutes (longer if colder) the clutch will begin to cycle in & out. After a short time it will cycle out completely and the roar will be gone. If the fan never roars when cold, my guess is it's bad. Checking if it comes in at the right temp is rather tricky. According to the book you're supposed to measure the temp of the air flowing through the rad in front of the clutch. If the temp gets too high before it cycles in, it's bad. Usually when it gets really hot outside and you've been running hard, watch the fan. If it looks like it is turning a lot slower than the engine, it might be bad. Sometimes they are so bad you can grab the fan blade and stop it while the engine is idleling. DO NOT TRY THIS!!!!!!!!!!!!!!!!! Do Not buy the non-stat clutches. Also if you buy too much of a "heavy duty" clutch, your fan blades won't heat up the fluid in the stat enough and the clutch will never cycle out. Then no one will hear your daul exhaust because all they hear is the fan roaring. Steve __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

03-20-2003, 02:38 PM	#6
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	By regular fan do you mean one without any clutch? Steve __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

03-19-2003, 01:50 AM	#5
Lightspeed Registered User Join Date: Oct 2002 Location: Virginia Posts: 226	is it hard to switch from a clutch type fan to just a regular fan?

03-20-2003, 03:35 PM	#7
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	Could you swap from the stock 16" clutch fan to a 16" electric fan and still have adequite cooling? Thanks HotRod __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/



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