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| Fan clutch [message #147584] |
Sun, 23 October 2011 20:27  |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
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I am just getting back into the GMC. Here is a question about the fan clutch operation. I have a cold engine so I step on the gas to set the automatic choke. I crank it over and the engine starts. I have the engine cover off and notice the fan clutch is engaged immediately which blows a heavy wind back into my face. I thought I remembered the fan clutch was not supposed to engage until the engine temp reached a certain level. I think my clutch is stuck on all the time but what is the correct operation? I know I should remember this but I did recently have my 70th birthday so I know my brain cell capacity is waning.
Thanks
Bob Sobrito
78 Palm Beach
La Mesa, Ca
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| Re: [GMCnet] Fan clutch [message #147585 is a reply to message #147584] |
Sun, 23 October 2011 20:30  |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
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Here is another question. I notice my signature says "77 Kingsley". How do I edit it to show "78n Palm Beach"?
Thanks again.
On Oct 23, 2011, at 6:27 PM, Bob Sobrito wrote:
>
>
> I am just getting back into the GMC. Here is a question about the fan clutch operation. I have a cold engine so I step on the gas to set the automatic choke. I crank it over and the engine starts. I have the engine cover off and notice the fan clutch is engaged immediately which blows a heavy wind back into my face. I thought I remembered the fan clutch was not supposed to engage until the engine temp reached a certain level. I think my clutch is stuck on all the time but what is the correct operation? I know I should remember this but I did recently have my 70th birthday so I know my brain cell capacity is waning.
> Thanks
> --
> Bob Sobrito
> 77 Kingsley
> La Mesa, Ca
> _______________________________________________
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Bob Sobrito
78 Palm Beach
La Mesa, Ca
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| Re: [GMCnet] Fan clutch [message #147596 is a reply to message #147594] |
Sun, 23 October 2011 20:52 |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
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Thanks Rob.
On Oct 23, 2011, at 6:45 PM, Rob Mueller wrote:
> Bob,
>
> While logged in to the Forum click on:
>
> Control Panel
>
> Account Settings
>
> Scroll down to:
>
> Preferences
> Signature
>
> You'll see your signature to the right.
>
> Regards,
> Rob M.
>
>
> -----Original Message-----
> From: robert sobrito
>
> Here is another question. I notice my signature says "77 Kingsley". How do I edit it to show "78n Palm Beach"?
> Thanks again.
>
>
> _______________________________________________
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Bob Sobrito
78 Palm Beach
La Mesa, Ca
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| Re: [GMCnet] Fan clutch [message #147602 is a reply to message #147585] |
Sun, 23 October 2011 21:09 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bob, the fan clutch should engage briefly upon engine startup when cold.
After a short time (they all operate a little differently so I can't give
you an exact time), the silicone substance that is contained within the
clutch will become quite fluid and the fan will slow down. When the engine
air temperature coming back from the radiator reaches the lockup design
temp, the silicone substance becomes less fluid like and the clutch again
locks up. When the air moving through the radiator cools off sufficiently,
the reverse happens and the clutch again slows down. Experience has shown
that each clutch's lockup and freewheel points are kinda unique to that
clutch. It is not an exact science. Steve Ferguson designed a test rig for
fan clutches and tested many or them and numerous brands. Some tested OK,
many did not. No particular brand outperformed the others as I recall. Many
are made by the same Mfg and boxed in different vendors packages. What I
would call a can of worms.
In any event, your clutch sounds like it is working like it should. If it
fails to lockup when the engine is very hot, then is when you should replace
it. Also if it fails to unlock, it should be replaced. Hope this helps.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Oct 23, 2011 at 6:30 PM, robert sobrito <rssbob@cox.net> wrote:
> Here is another question. I notice my signature says "77 Kingsley". How
> do I edit it to show "78n Palm Beach"?
> Thanks again.
>
> On Oct 23, 2011, at 6:27 PM, Bob Sobrito wrote:
>
> >
> >
> > I am just getting back into the GMC. Here is a question about the fan
> clutch operation. I have a cold engine so I step on the gas to set the
> automatic choke. I crank it over and the engine starts. I have the engine
> cover off and notice the fan clutch is engaged immediately which blows a
> heavy wind back into my face. I thought I remembered the fan clutch was
> not supposed to engage until the engine temp reached a certain level. I
> think my clutch is stuck on all the time but what is the correct operation?
> I know I should remember this but I did recently have my 70th birthday so I
> know my brain cell capacity is waning.
> > Thanks
> > --
> > Bob Sobrito
> > 77 Kingsley
> > La Mesa, Ca
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Fan clutch [message #147615 is a reply to message #147602] |
Sun, 23 October 2011 21:27 |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
Karma: 0
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Thanks James. I got it.
On Oct 23, 2011, at 7:09 PM, James Hupy wrote:
> Bob, the fan clutch should engage briefly upon engine startup when cold.
> After a short time (they all operate a little differently so I can't give
> you an exact time), the silicone substance that is contained within the
> clutch will become quite fluid and the fan will slow down. When the engine
> air temperature coming back from the radiator reaches the lockup design
> temp, the silicone substance becomes less fluid like and the clutch again
> locks up. When the air moving through the radiator cools off sufficiently,
> the reverse happens and the clutch again slows down. Experience has shown
> that each clutch's lockup and freewheel points are kinda unique to that
> clutch. It is not an exact science. Steve Ferguson designed a test rig for
> fan clutches and tested many or them and numerous brands. Some tested OK,
> many did not. No particular brand outperformed the others as I recall. Many
> are made by the same Mfg and boxed in different vendors packages. What I
> would call a can of worms.
> In any event, your clutch sounds like it is working like it should. If it
> fails to lockup when the engine is very hot, then is when you should replace
> it. Also if it fails to unlock, it should be replaced. Hope this helps.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Sun, Oct 23, 2011 at 6:30 PM, robert sobrito <rssbob@cox.net> wrote:
>
>> Here is another question. I notice my signature says "77 Kingsley". How
>> do I edit it to show "78n Palm Beach"?
>> Thanks again.
>>
>> On Oct 23, 2011, at 6:27 PM, Bob Sobrito wrote:
>>
>>>
>>>
>>> I am just getting back into the GMC. Here is a question about the fan
>> clutch operation. I have a cold engine so I step on the gas to set the
>> automatic choke. I crank it over and the engine starts. I have the engine
>> cover off and notice the fan clutch is engaged immediately which blows a
>> heavy wind back into my face. I thought I remembered the fan clutch was
>> not supposed to engage until the engine temp reached a certain level. I
>> think my clutch is stuck on all the time but what is the correct operation?
>> I know I should remember this but I did recently have my 70th birthday so I
>> know my brain cell capacity is waning.
>>> Thanks
>>> --
>>> Bob Sobrito
>>> 77 Kingsley
>>> La Mesa, Ca
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
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Bob Sobrito
78 Palm Beach
La Mesa, Ca
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| Re: Fan clutch [message #147710 is a reply to message #147584] |
Mon, 24 October 2011 18:32 |
kingd
Messages: 592
Registered: June 2004
Karma: 2
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Senior Member |
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James H, not to be picky, but it is NOT the viscosity of the fluid that turns the fan on and off. There is a bi-metallic coil on the front of the clutch that turns a shaft that goes into the front of the clutch. The position of that shaft controls where the fluid is in the housing and that controls if the fan is on or off. What is inside the housing actually sounds to be resonably sophisticated.
DAVE KING
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
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| Re: Fan clutch [message #147726 is a reply to message #147584] |
Mon, 24 October 2011 20:17 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Yes when it sits the fluid distributes by gravity between the working chamber and the storage chamber so it's "half" engaged but as it's cold, it's fairly locked up. (A clutch that does NOT do this has most likely lost some fluid and is probalby going to need replacement.) The bimetalic spring when cold has rotated the valve to pump the fulid to the non working chamber, so after like a block or so of driving the fluid redistributes and goes back to the most free wheeling mode. As post radiator air temp rises, the bimetalic spring rotates the valve and the rotational pumping action sends some fluid to the working chamber, speed increases as needed. The difference between in to out speed required the heat sink on the clutch. At some point if pulling a grade or going to a lowspeed after a road load speed (loss of natural convention from vehicle movement at speed) the clutch will engage as temp in the post radiator area rises. The way I understand it it modulates until at some point it approaches 1 to 1 (or less depending on the "duty" type of the clutch you have bought). This is described in GM sevice manuals as "fan roar". In some extreme condition cases at highway speeds it will engage and cycle as needed and the temp guage will drop rapidly during the "roar" period, then slowly climb back up till it engages and repeats. It's amazing how much more air than the say 60MPH air coming in the front it can move and the rapid cooling it provides. We just got a new Peterbilt truck and the clutch is computer (electric) driven with a manual lockup override switch on the dash. It's either on or off and no inbetween. At road speeds it cycles on and off abruptly, even with the large flat open radiator area at speed it is still required and really drops the temp back to the stat point rapidly. You would thing road speed would provide enough cooling, but in heavy vehicles, road load is greater and this alone is often not enough air flow.
John Lebetski
Woodstock, IL
77 Eleganza II
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| [GMCnet] HEI distributor question. [message #147999 is a reply to message #147584] |
Thu, 27 October 2011 21:22 |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
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I want to do buy parts for a tune up. I have a 78 and I notice the GMCMI parts interchange index lists parts for (75 - 78) except (california) and then lists parts for (78) California. How do I know by looking at my HEI distributor whether or not I have a california or "all other" system?
Thanks.
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Bob Sobrito
78 Palm Beach
La Mesa, Ca
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| Re: [GMCnet] HEI distributor question. [message #148026 is a reply to message #147999] |
Fri, 28 October 2011 06:34 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Sir: section 6-T
http://www.bdub.net/manuals/X7725/X7725.pdf
Calif has 2 charcoal canisters, distributor adv has 2 vacuum lines, intake has 2 vacuum trees ( one hi temp, one low temp).
| rssbob wrote on Thu, 27 October 2011 22:22 |
I want to do buy parts for a tune up. I have a 78 and I notice the GMCMI parts interchange index lists parts for (75 - 78) except (california) and then lists parts for (78) California. How do I know by looking at my HEI distributor whether or not I have a california or "all other" system?
Thanks.
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C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] HEI distributor question. [message #148036 is a reply to message #148020] |
Fri, 28 October 2011 11:11 |
rssbob
Messages: 259
Registered: January 2004
Location: La Mesa, Ca. (San Diego a...
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Thanks Jim and charles.
On Oct 27, 2011, at 10:18 PM, James Hupy wrote:
> The simple way is to kneel down by the passenger side front wheel and look
> just behind the inner fender. If you have two charcoal cannisters, your
> coach is California Equipped.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Thu, Oct 27, 2011 at 7:22 PM, robert sobrito <rssbob@cox.net> wrote:
>
>> I want to do buy parts for a tune up. I have a 78 and I notice the GMCMI
>> parts interchange index lists parts for (75 - 78) except (california) and
>> then lists parts for (78) California. How do I know by looking at my HEI
>> distributor whether or not I have a california or "all other" system?
>> Thanks.
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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Bob Sobrito
78 Palm Beach
La Mesa, Ca
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