Home » Public Forums » GMCnet » [GMCnet] fan clutch mystery / theory
| [GMCnet] fan clutch mystery / theory [message #316429] |
Fri, 21 April 2017 23:41  |
Ek_Lektro
Messages: 167
Registered: March 2011
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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
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| Re: [GMCnet] fan clutch mystery / theory [message #316432 is a reply to message #316429] |
Sat, 22 April 2017 02:00  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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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
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| Re: [GMCnet] fan clutch mystery / theory [message #316435 is a reply to message #316432] |
Sat, 22 April 2017 06:45 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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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
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] fan clutch mystery / theory [message #316437 is a reply to message #316429] |
Sat, 22 April 2017 06:56 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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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.
On Sat, Apr 22, 2017 at 12:41 AM, Ek_Lektro wrote:
> ...
>
>
> 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)
> ...
>
>
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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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| Re: [GMCnet] fan clutch mystery / theory [message #316439 is a reply to message #316437] |
Sat, 22 April 2017 07:16 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Here is the chart that Ken was referring to.
http://gmcmotorhome.info/engine.html#sender
J.R. Wright
GMC GreatLaker
TZE Zone Restorations
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Apr 22, 2017, at 7:56 AM, Ken Henderson wrote:
>
> 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.
>
>
>
> On Sat, Apr 22, 2017 at 12:41 AM, Ek_Lektro wrote:
>
>> ...
>>
>>
>> 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)
>> ...
>>
>>
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] fan clutch mystery / theory [message #316443 is a reply to message #316429] |
Sat, 22 April 2017 09:15 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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
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| Re: [GMCnet] fan clutch mystery / theory [message #316446 is a reply to message #316429] |
Sat, 22 April 2017 10:55 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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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.
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| Re: [GMCnet] fan clutch mystery / theory [message #316448 is a reply to message #316429] |
Sat, 22 April 2017 11:15 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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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
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| Re: [GMCnet] fan clutch mystery / theory [message #316449 is a reply to message #316429] |
Sat, 22 April 2017 11:19 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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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
Foolish Carriage, 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
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| Re: [GMCnet] fan clutch mystery / theory [message #316450 is a reply to message #316448] |
Sat, 22 April 2017 11:25 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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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
On Apr 22, 2017 9:16 AM, "Tyler" wrote:
> 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
>
> _______________________________________________
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>
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| Re: [GMCnet] fan clutch mystery / theory [message #316464 is a reply to message #316429] |
Sat, 22 April 2017 12:26 |
Ek_Lektro
Messages: 167
Registered: March 2011
Karma: 2
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Thanks for all the replies and suggestions…
I should have added to my original email that besides the hill-cresting situation,
the fan clutch is engaged about 65% of my drive time. In other words it is on more than its off!
If it was a 95 degree summer day or i was climbing a lot of hills, i’d be thankful for that,
but this was on mostly straightaways and a 70 degree spring day
The fan clutch itself was my immediate suspicion (until the mechanic mentioned the possibility of water pump, and so i had to ask some opinions on that… ). Its not a Hayden, rather AutoZone’s Duralast (worse?) Heavy Duty. Not sure if i can get AC Delco down here in Tijuana.
My ’76 455 has a 7 blade fan, so perhaps i should be switching to Severe Duty?
I”m going down to AutoZone today to compare numbers and see if the correct fan clutch was in the box to begin with!
Am i correct in assuming that a Severe Duty would engage less often? Maybe my coach is a candidate for this?
Sure, i’d rather protect the engine than worry about a bit of noise and crappy fuel economy, but….
BTW: The ducting between the radiator and fan is all intact. Coolant level is normal, however there’s a chance that the ratio might be a bit high on the water to coolant side of things… since i added a half gallon of distilled water after a fixing a leak; but i can’t imagine that’s gonna tip the scales that much.
After they did the head gaskets and main seal last November, driving home, besides the fan clutch, i did notice a bit of new minor “noise” up front, but it was hard to tell if this was just belt noise. didn’t sound like a water pump bearing, so didn’t worry about it.
And as for the temperature sensor, i did replace it with the TU5 unfortunately, OEM, but i am accustomed to what the readings should be,
and its been below normal (below 1/4) for quite a while. So i’ll look into the wiring. Thanks for that tip, Ken
OK, standing by for any possible new revelations…
From a noisy garage in TJ,
cheers!
Greg
> 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.
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| Re: [GMCnet] fan clutch mystery / theory [message #316473 is a reply to message #316471] |
Sun, 23 April 2017 07:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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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
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| Re: [GMCnet] fan clutch mystery / theory [message #316476 is a reply to message #316429] |
Sun, 23 April 2017 07:43 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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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
2017 Winnebago 29VE
Winter Springs FL
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| Re: [GMCnet] fan clutch mystery / theory [message #316481 is a reply to message #316476] |
Sun, 23 April 2017 08:59 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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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.
On Sun, Apr 23, 2017 at 8:43 AM, Bob Heller wrote:
> ...
>
> 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.
> ...
>
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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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| Re: [GMCnet] fan clutch mystery / theory [message #316483 is a reply to message #316429] |
Sun, 23 April 2017 10:18 |
Mike S
Messages: 82
Registered: February 2017
Location: Vero Beach, FL
Karma: 3
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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.
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| Re: [GMCnet] fan clutch mystery / theory [message #316486 is a reply to message #316483] |
Sun, 23 April 2017 10:47 |
JohnS
Messages: 126
Registered: December 2014
Location: Vacaville, CA
Karma: -2
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Senior Member |
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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, ncserv@aol.com;
78 Buskirk stretch, "What were we thinking?"
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