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| [GMCnet] Re: Radiator cooling fan [message #366847 is a reply to message #366844] |
Fri, 17 September 2021 10:38   |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Reminds me of our trip across the Texas Panhandle in the summer of about
'81. We had a '75 Titan motorhome with a Chrysler 318 engine. We were
cruising along pretty nicely, then I slowed down below 50 mph, and the
transmission downshifted! I finally found that it did it pretty
consistently: Below about 50 mph it would downshift to 3rd gear. At
higher speeds it upshifted again. Finally, we arrived at Palo Duro Canyon
for the night. I found a 'phone (no cells in those days) and called my old
F101B pilot buddy in NC, who owned an RV dealership: "What should I tell
the shop when I take this darned thing in tomorrow?" He got a big kick out
of that question: "I think your fan clutch is working just fine!"
That one was electrically controlled, so the next morning I added a control
switch. Sure 'nuff, with that, I could "upshift" at will! :-)
Ken H.
On Fri, Sep 17, 2021 at 11:02 AM James Hupy wrote:
> I will try to explain this one more time. Both Steve Ferguson and I have
> presented seminars on this subject more than once, and probably will again,
> if the Good Lord allows me enough time.
> Fan clutches are filled with a very special silicone fluid that gets
> more viscosity when it is heated, unlike hydrocarbon and synthetic oils
> that thin out, or less viscous, when they are heated. If you look at the
> finned surface of a fan clutch, you will see in the center of it a flat
> shaped spring coiled in a circle with several wraps. One end is anchored to
> the clutch body, and the other end is connected to linkage that disappears
> inside the clutch. That linkage operates a valve that circulates that
> viscous fluid to expose it to more driven fin like elements, and that in
> turn makes the clutch "lock up" or drive the fan at a speed higher than it
> is when the spring is not expanded. Clear as mud, right?
> Simple answer, is that it is hot air that has an effect on the spring!
> NOT HOT COOLANT. HOT COOLANT heats the air that passes through the
> radiator, and that activates the spring, etc, etc.
> Remember this. The higher the air flow volume through the radiator,
> the less heat is concentrated in a smaller volume of air. So, that is why
> the clutches seldom lock up at highway speed, and more when the coach is
> moving slower. Also, the clutch is behind the curve, the coolant has
> already gained more heat, reflected in your coolant temp gage indication,
> before the air gains enough temp to activate that little spring.
> More to it than space allows here, so, catch me at a rally someplace,
> and I will explain in detail.
> Jim Hupy
> Salem, Oregon
>
> On Fri, Sep 17, 2021, 5:22 AM tom geiger wrote:
>
>> Todd, just went out and tested the fan clutch and it did spin with some
>> resistance so I guess its working then. It is for sure spinning the fan
>> when
>> I first start it up. The aftermarket temp gage shows temps in and around
>> 200+ as my OEM gage shows the 1/4 mark. I may be fine on engine temp but
>> wanted to check with a accurate temp gage test kit to make sure. I’ve
>> been having what seems to be knocking that seems to be starting up when
>> engine is at full temp. I just want to make sure the engine is operating
>> at proper temps.
>>
>> Thanks,
>> TG
>> --
>> Tom Geiger
>> 76 Eleganza II
>> KCMO
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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