fan clutch mystery / theory

[ek_lektro]

hello GMC Amigos,
i’m writing from a garage down in Tijuana, where i got some good mechanical work done last year,
and where i’m currently getting a bunch more stuff done before my 1yr Mexican RV insurance expires
Back in November, they replaced the head gaskets, front engine seal and put in a new fan clutch
(Duralast AutoZone 22045 on a 455 engine.. apparently they retired some of the older part numbers, but i think this one cross references with 2747)
On the ride home, i was puzzled by the times that the fan clutch would run vs. not run.
I’d be climbing a hill with no fan clutch noise, but then once i crested the hill and started to let off on the accelerator, the fan clutch would engage… the opposite of what we’d expect!

The mechanic here thinks its a failing water pump. From what i understand from his explanation; apparently with a bad water pump, it will only push water during acceleration(?) So once i’ve crested a hill, and let go of the accelerator, there’s reduced water flow, and the engine heats up… and the fan clutch comes on. Does this make sense? Or are there other things to check?

I should add: at the time of the fan clutch replacement, we also replaced the engine temperature sensor, since it’d always read way too cool (almost completely at the bottom) for way too long… perhaps only coming up to normal middle temperature after 45 minutes of driving. Well, replacing the sensor didn’t fix this issue (so the gauge itself is probably bad(?); But the point is, right now we can’t use the temp gauge as a guide for when the fan clutch should engage.

If replacing the water pump is the recommended course of action, i’m guessing that AutoZone down here will have similar stock to the US stores.. and that i should cross reference NAPA 43100 or AC Delco 251-231

As for the temperature gauge, Is there a replacement for the original? Or is it time to switch to digital?
(Lastly, i’m pretty sure we replaced the thermostat a year ago)

Any and all advice appreciated, cheers!
Greg

 

[Ken B]

I'm just thinking out loud here.

1. On the way down hill the clutch turns on.
Well, the fan turns on by sensing the heated air coming off of the radiator. So if there were less coolant flow caused by a bad pump when going down
hill then there is less heat being transferred. The fan should not turn under that scenario. I do not buy that explanation.

2. There is not much to go bad in a water pump. There is a impeller inside, a shaft, a bearing, a seal, and a pulley to turn the shaft and
impeller. I guess the impeller inside that moves the coolant could over time disintegrate (I've never seen this). The pulley or belts could wear but
there are 3 belts there. All of these other than the belts are not likely.

If you have an original pump then it has a 4.25" impeller inside. If the pump has been changed then it is possible someone installed one with a much
smaller impeller. That same pump casting was used with various sized impeller pumps. I always use a pump with a 4" or larger impeller. I doubt
that you have a bad pump.

3. Since the temperature sender has been replaced, I doubt that the temperature gauge is a problem. There is a wire that runs from the plate where
the temperature gauge is mounted to the plate where the isolator is mounted under the hood. This wire supplies ground to all of the lights and gauges
on the dash. This wire occasionally loosens up on the dash end. You could temporarily run a second wire with a pair of alligator clips between those
two points to verify if the other existing ground wire is your problem. There is also a second wire from the isolator plate to the negative terminal
of the engine battery that could be the problem.

You could also temporarily install a second non-electric gauge and see if it reads similar to your existing electric one.

4. We once met a GMCer on the way to a rally out west. He was stopped on the side of the road over heated. We got him filled up with coolant and
off we went on the 2 days drive. His engine would run fine under load going down the road but every time he slowed down or stopped it would get hot
and sometimes boil over. It had 3 of us in the convoy confused but he made it to the rally and back home again a week later. He later ran a
compression test and found a leaking head gasket. He replaced the head gasket and never had the problem again. I'm not saying this is your problem
but you have similar symptoms.

5. If that fan clutch is made by Hayden (a 2747), I would get rid of it and get an AC Delco one. I once fought intermittent turn off and and
especially turn on problems with 6 different Hayden clutches 14 years ago. Replacing it with an AC Delco heavy duty (NOT SEVERE DUTY) clutch took
care of the problem.

All of these are kind of random thoughts but maybe they will help you.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[thomas phipps]

Ken's point #1 is dead on. My GMC fan clutch would engage after cresting a hill quite often, especially down here in the warm South.
Tm, MS II
--
1975 GMC Avion
KA4CSG

 

[Ken H.]

Greg,

A couple of thoughts:

1. Has the temperature sender been changed to the NAPA TS-6469? If not,
1/2 scale is HOT. Somewhere on Gene Fisher's site there's a table
comparing the OEM and 6469 -- you DON'T want the OEM sender.

2. Some have reported problems similar to yours being solved by adding
ductwork between the grille and the radiator to eliminate air bypassing the
radiator core.

3. I agree with Ken B. about the water pump -- very unlikely that it's the
problem, else the overheating would occur during the climb.

HTH,

Ken H. http://www.gmcwipersetc.com

> ​...
>
>
> As for the temperature gauge, Is there a replacement for the original? Or
> is it time to switch to digital?
> (Lastly, i’m pretty sure we replaced the thermostat a year ago)
> ​...
>
>

 

[wrightjohn 2646]

Here is the chart that Ken was referring to.

http://bdub.net/gmcmotorhome.info/engine.html

J.R. Wright
GMC GreatLaker
TZE Zone Restorations
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

>
> Greg,
>
> A couple of thoughts:
>
> 1. Has the temperature sender been changed to the NAPA TS-6469? If not,
> 1/2 scale is HOT. Somewhere on Gene Fisher's site there's a table
> comparing the OEM and 6469 -- you DON'T want the OEM sender.
>
> 2. Some have reported problems similar to yours being solved by adding
> ductwork between the grille and the radiator to eliminate air bypassing the
> radiator core.
>
> 3. I agree with Ken B. about the water pump -- very unlikely that it's the
> problem, else the overheating would occur during the climb.
>
> HTH,
>
> Ken H. http://www.gmcwipersetc.com
>
>
>

>
>> ​...
>>
>>
>> As for the temperature gauge, Is there a replacement for the original? Or
>> is it time to switch to digital?
>> (Lastly, i’m pretty sure we replaced the thermostat a year ago)
>> ​...
>>
>>

 

[john r. lebetski]

Start by insuring all air is out of system. I don't buy the water pump theory unless the impeller has rusted or worn away. The clutch works by temp
but also is a power transfer limiting device. On a hot day after cruising on the highway mine will come on when I lift to hit the exit ramp - even
though forward vehicle speed (ram effect) is still high. My theory is because RPM of engine drops the differential between slip and transmission of
power gets smaller so it allows it to lock up at that speed, My testing shows that there are huge temp swings in the air stream flowing to the fan
clutch (signal) whereas water temps move in a very stable manner. Being low on coolant will exasperate the air temperature swings and top portion of
core will be sending "cool" outside air into the signal mix.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[terry1]

Jim and Bob have the correct answer on the reply to this post from the email; sounds like you are experiencing the time delay between heat buildup in
the engine and the transfer of that heat to the air stream coming through the radiator which controls the engagement of the fan clutch. You may also
have to drop the rpm once or twice on the way up a LONG hill to make it easier for the clutch to engage on the way up, but that would seem to me to
indicate a sub-par clutch mechanism, unless it is designed to slip at high RPM differential to reduce its power requirement (on a downshift passing
maneuver, for example).
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

 

[tyler]

This is fascinating - I put that same fan clutch on last year. I blocked my intake exhaust passages a few weeks ago. Four hundred mile trip last week
many terrains, low 80's highest ambient temperature and it acted just like Greg described. I clearly had heat in the wrong places before the intake
block off, but the fan on this last trip almost seemed counterintuitive! It literally would turn on the roar when i would lift my foot out of the gas
after even a moderate pull. It stayed on full roar if i sustained mph over 63. It would turn on very nicely (still loud) at stoplights and run for a
few hundred yards, but overall I did not like it.

I was guessing that my add on transmission cooler might be moved to the bottom to keep that heat from the direct center, but if these particular
clutches are just wonky, I might put on the Carquest (Advance) clutch that I found last year that was actually described as heavy duty (not standard
or severe duty)
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[johnny]

Speak to Jimmy The K - he's shown an electrically operated clutch model. I'll be adding one to my coach as soon as the transmission goes back in. As
to noise, the thing is so dam' noisy now it isn't going to make much difference.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[Jim Hupy]

Replace the fan clutch. I replaced 3 identical part numbers in a row before
I got one that works like I prefer. Also inspect for obstructions to the
airflow into and out of the engine compartment, as well as leaky silicone
fluid from the fan clutch. It will collect road dirt and delay movement of
the lock up feature. Critter nests will do the same thing.
Jim Hupy

> This is fascinating - I put that same fan clutch on last year. I blocked
> my intake exhaust passages a few weeks ago. Four hundred mile trip last week
> many terrains, low 80's highest ambient temperature and it acted just like
> Greg described. I clearly had heat in the wrong places before the intake
> block off, but the fan on this last trip almost seemed counterintuitive!
> It literally would turn on the roar when i would lift my foot out of the gas
> after even a moderate pull. It stayed on full roar if i sustained mph over
> 63. It would turn on very nicely (still loud) at stoplights and run for a
> few hundred yards, but overall I did not like it.
>
> I was guessing that my add on transmission cooler might be moved to the
> bottom to keep that heat from the direct center, but if these particular
> clutches are just wonky, I might put on the Carquest (Advance) clutch that
> I found last year that was actually described as heavy duty (not standard
> or severe duty)
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>

 

[a.]

> Speak to Jimmy The K - he's shown an electrically operated clutch model. I'll be adding one to my coach as soon as the transmission goes back in.
> As to noise, the thing is so dam' noisy now it isn't going to make much difference.
>
> --johnny
That would be the way to go. Have the clutch engage based on coolant temp rather than whatever arbitrary temp the clutch thinks the engine compartment
is. I sort of wonder if the design was inspired by a thread back in 2012.

http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&goto=175015&rid=2083
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"When I grow up I am going to be a curmudgeon."

 

[Tom Pryor]

So folks we have again arrived at a subject that I presented at the
Mansfield Rally this past spring. The reality is that WE CAN NO LONGER
TRUST THE BI METAL SPRING FAN CLUTCHES manufactured offshore and supplied
to the automotive stores.

After the Radiator expansion tank blew up in my face on the way to the
South Dakota I made it my passion to Re purpose an Electronic Viscous
Clutch (EVC) For our 403, 455 Engines. That System is now available from
Applied GMC. It is pricey, and not for everyone. Why so Much? The EVC
technology in todays engines are significantly more reliable and gone are
the days of a $50 fan clutch anyway.

System Highlights:

A. The new 20" Fan/Clutch is an assembly of European decent. It is
guaranteed to decouple within 2 Minutes at 2500 rpm.
The fan clutch is supplied with the means to thread the 40mm LH
thread to our water pump flange.
Minor fan shroud trimming is required but the Horse Collar cannot be
used.
B The fan Controller is of patented design and is operator adjustable.
Shuts off at 10 Degrees below the set point.
C The temperature sensor is installed in the Christmas tree hole on the
right side of engine intake manifold and feeds the controller with
temperature data.
D The fan clutch can also be engaged with a dash mounted switch in
anticipation of increased cooling requirements.

If it is important to you to know that your engine Fan is engaging when the
coolant temperature needs attention this kit will be most helpful and
reliable.

SEE: http://appliedgmc.com/prod.itml/icOid/1867

--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

Living on a waterfront is not a matter of life or death. Its more
important than that.

 

[thomas phipps]

7 Blade fan is correct. Do not lose it.
Tom, MS II
--
1975 GMC Avion
KA4CSG

 

[Ken B]

OK, Here goes.

The fan clutch (and fan) are only there for abnormal cooling situations. This would include things like extended idling in city traffic or pulling a
long hill while towing something. Other than abnormal situations it should remain off while going down the road. If you require a severe duty clutch
to cool the radiator of a GMC then you have other cooling system problems like a plugged radiator.

The on/off temperature of the clutch is sensed by a coil spring on the front of the clutch that determines the cooling ram air temperature coming off
of the back of the radiator. When the air off of the radiator gets too hot, then the clutch kicks in and pulls more air through the radiator to try
to cool down the radiator. The clutch is concerned with radiator coolant temperature and cooling efficiency and not directly the engine temperature
although they the are some what related.

The problem that I had with 6 Severe and Heavy Duty Hayden clutches across 2 years of trouble shooting with Hayden Engineering was the clutches came
on much too often.

Hayden sent me 5 different replacement clutches across the two years time trying to fix their problem. After two years in one of my many
conversations with Hayden Engineering they admitted to me that they had reduced the turn on temperature on their line of clutches. That reduction was
what they then thought was causing my problem in a GMC.

They asked me to modify the temperature sensing spring attachment with a dremnel tool to increase the turn on temperature. I refused at that point,
trashed the 5 replacements that I had, and returned one for a refund. I was fed up with what they had put me through for 2 years.

A well respected GMCer from BC, Denny Allen, suggested that I go to a Heavy Duty Delco clutch. I called AC Delco Engineering and got their
recommendation. They based their recommendation on the size and pitch of the fan plus they looked up the specs of the OEM GMC clutch. Their
recommendation matched Denny's so I got an AC Delco Heavy Duty 15-4208 (now obsolete) clutch. It has been in there for 14 years.

A properly operating severe duty clutch will come on at the same temperature, but will move more air. It also is noisy and needs to have very good
condition fan belts. I was warned by Ac Delco Engineering not to use it in a GMC with less than two drive 1/2" belts, but many people here have
successfully used them and at least two of our GMC Vendors sell them.

On the gauge sending unit. It needs to be changed as per Colonel Ken's recommendation. It is impossible to see any real temperature changes using
the OEM one until it is too late. Those senders are very cheap and it is a few minute job to unscrew one and install the replacement.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[bob heller]

Greg,

I put one of these 22045 Autozone fan clutches on my GMC in January. Mine behaves the same way. It operates a bit differently than the older 22747
clutches. I noticed it looked substantially different and is made in Korea (not China).

My experience with the older 22747 clutch was that, generally, it was engaged far too much. Some clutches were worse that others, the really bad ones
I would 'readjust' the thermostat spring a bit to change the engage temperature. The 22747 also didn't last more than about a year to 18 months before
they started leaking fluid or getting what I thought was too much play at the fan. Then I would take it back to Autozone and get yet another 22747.
Apparently Autozone has discontinued the 22747 and says to use the 22045 in it's place. The last warranty replacement this past January they charged
me the difference between the two clutches (about $11, IIRC) and now I will get 22045's when they fail.

The 22045 keeps the engine cool and the a/c working just fine, it just engages a bit more than I would like but it's not too bad. If I get bored some
day I might jimmy the thermostatic spring a bit but for now it works pretty good just as it came out of the box. What I've noticed (and apparently you
have too) is that on a warm day, when slowing the engine down from cruising speeds (about 2600) to a lower speed (about 1600) the fan noticeably
speeds up, sometimes for a few seconds, sometimes for a lot longer. The 22747 clutch did not do this, or if it did it was not really noticeable.
That's just the way it is with the 22045 clutch.

I can't complain too much about all of the Autozone fan clutches I've put on my GMC because in 10 years I've paid for one 22747 and then the $11
difference for the 22045, well under a hundred bucks total. The labor is free (me). As long as Autozone keeps giving me warranty replacements I'm
happy.
--
Bob Heller
1974 X-Canyonlands 26ft
Original 455 exc for timing chain,
Rockwell intake, valve covers. 141k miles.
Winter Springs FL

 

[Ken H.]

Bob,

I don't understand AZ CHARGING you for providing a warranty replacement. I
went through a similar experience with them a month or so ago. I had what
MAY have been an AZ 22747 (neither I nor they could determine just what it
was, but their computer said I'd bought one of those) which they replaced
with a 22045. As you report, that one's price was higher -- so they posted
a mark-down on it and gave it to me. Seems to me that was the correct
action, 'cause THEY are the ones who needed to fulfill their warranty
commitment. Sometimes you have to be stubborn with them, but not this time.

Ken H.

> ​...
>
> Apparently Autozone has discontinued the 22747 and says to use the 22045
> in it's place. The last warranty replacement this past January they charged
> me the difference between the two clutches (about $11, IIRC) and now I
> will get 22045's when they fail.
> ​...
>

 

[mike sadlon]

I would suggest looking at your under hood air flow also. The single biggest cooling improvement I made was adding side and top baffles between the
front grill and radiator. Stopped all fan noise unless in traffic.
Second, was the vents near the front wheels. That help the interior of the coach be cooler.

 

[SteveW]

Thank you everyone... I'm working my cooling system too.

What's the recommended fan clutch to put in front of the 11 blade nylon/plastic fan - all behind a new aluminum radiator ?

Steve W
1973 23'
Southern California

 

[Jim Hupy]

Look at the front of the coach on a 77 or 78 and you will see what GM did
to improve the airflow through the radiator and A/C condensor, also the
shroud around the 7 blade fan is different than the earlier coaches. Ditto
what was said about the "shark gill" vents. They really do work well.
Jim Hupy

> I would suggest looking at your under hood air flow also. The single
> biggest cooling improvement I made was adding side and top baffles between
> the
> front grill and radiator. Stopped all fan noise unless in traffic.
> Second, was the vents near the front wheels. That help the interior of the
> coach be cooler.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[john shutzbaugh]

Best cooling improvement I have made is to install an air dam at the bottom of the radiator. I copied the designs of JR wright and Armand Minnie.
JR's unit can be bought from Applied, and Armand details his design and experiences on his website. My experience with this dam is that the fan
clutch only comes on in hot slow traffic and on long, hard, hot grades.
--
John Shutzbaugh, Vacaville, CA;
77 Eleganza, bought it new, can't blame PO, and
78 Buskirk stretch, "What were we thinking?"