Conference ssdevo::4wd

I have a '96 Blazer LS and experience the same thing intermittently under the 
conditions you describe.  I sense a loss of acceleration power at the same 
time, though, and eventually the sound just suddenly dies and all operation 
returns to "normal."  I saw a "loss of power" technical service bulletin on 
the Alldata web site, but haven't talked to my dealer about it yet.

Jay

Well, prompted by the base note, I finally spoke to the service writer at the 
dealership where I bought my '96 Blazer LS, and he said the same thing- fan 
noise.  I'll keep monitoring- more closely now- too see if there really is no 
loss of power, just noise.

Jay

    ref 1638.1-2
    
    What you are hearing is the high pitch of the fan pulling lots o' air.
    What you are hearing when it suddenly goes away once you are underway
    is it's thermostatically operated clutch taking the fan out of straight
    drive and into a fluid-coupling drive that allows it to semi-freewheel
    and not pull so much air.  The semi-freewheel also frees up as much 
    as 15 extra HP for the ENGINE to use.
    
    The fan should run kinda noisy on first startup even in Winter
    and then quiet down in something less than 2 minutes... again, it's the
    clutch letting go into freewheel/fluid coupling drive instead of locked
    up in straight drive.
    
    The clutch will also 'cycle' on a hot day or while the vehicle is
    sitting and idling for extended periods.
    
    This design is the first truly automatic fan which has a high cooling 
    capacity (a' la very high pitch fan), yet only steals HP and moves 
    LOTS of air when it's needed.  The next generation of this concept is 
    the electric radiator fan which functions identically but is all 
    electric instead of the more rugged mechanical design... the HP loss 
    with electric fans is through loading the alternator.
    
    Anyway, what you're hearing is perfectly normal.  The only way to make
    it quieter is to look for a car fan that'll fit your clutch that has
    the 'staggered blade' design... three blades uniformly spaced opposing
    two evenly spaced blades with large-ish gaps between the two 'clusters'
    of blades.  This prevents what is known as 'beat frequency' from
    setting up among the 5 blades.  I won't go into the acoustical physics
    but suffice it to say, that style fan is about 1/2 as noisy as the one
    you have and still does the same job.  I'd check a boneyard for an
    older GM rear wheel drive car with all the toys, (Dinosaurus, Detroitus,
    Extinctus) for one of them.  The clutch and fan assembly should fit
    your water pump drive flange.  All you need to verify is the same
    diameter and no bent blades.  
    
    Next alternative is to remove the mechanical fan and install a HUGE 
    (17") electrical cooling fan and thermostatic switch. The fan's relay 
    should also be activated any time the AC clutch is activated just for
    that extra anticipative cooling boost when the air's on.
    
    As for the "Loss of Power" technical bulletins... black hole...don't
    even go there; it's  not relative.  That stuff's related to the electrical
    and engine management electronics, not a mechanically driven fan.
    
    If you don't want to tackle any of the above... learn to ignore it.
    
    Regards,

I, too, had this in my 95 Jimmy.  I also had this in my 88 Astro van
with the same 4.3L motor and same fan/clutch setup.  My son used
to refer to this noise as the "school bus sound".  On my Jimmy, it'd
do it mostly when cold, but it became very obvious when the noise
went away.  It sure FELT like you were losing power when the 
noise was on, and got more when the noise disappeared.  And it may
very well have been true, since it was driving the fan full-throttle until
the clutch let it free-wheel a bit.  But after 2 minutes or less it would
always quiet down, so I never worried about it.  If yours is noisy all the
time I'd have the dealer check to see if the clutch is always keeping the
fan running full-time (when it shouldn't).

andy

><<< Note 1638.4 by ZEKE::dmdg07.zko.dec.com::ASCHNEIDER "Andy Schneider - DTN 381-1696" >>>
>                   -< Same for me - even on an older Astro >-

>On my Jimmy, it'd
>do it mostly when cold, but it became very obvious when the noise
>went away.  It sure FELT like you were losing power when the 
>noise was on, and got more when the noise disappeared.  And it may
>very well have been true, since it was driving the fan full-throttle until
>the clutch let it free-wheel a bit.  But after 2 minutes or less it would
>always quiet down, so I never worried about it.  If yours is noisy all the
>time I'd have the dealer check to see if the clutch is always keeping the
>fan running full-time (when it shouldn't).

    I did a search on the internet for "clutch fan" and found the
    following.  It wasn't directly for the Blazer, but I would assume a
    similar setup as this (this was talking about a GM vehicle):

   "The mechanical fan used with the V08 cooling system contains a built-in
    thermostatic clutch which senses the temperature of air that has been
    drawn through the radiator. When the temperature of this air is below
    66 degrees C (151 degrees F), the clutch freewheels and limits the fan
    speed to 800-1,400 rpm. When the temperature rises above 66 degrees C
    (151 degrees F), the clutch begins to engage, and the fan speed
    increases to about 2,200 rpm."

    Other info I found described the system as having a bi-metallic spring
    which controls transfer of the clutch fluid from the free-wheeling side
    to the driving side of the clutch based on temperature of the air
    passing through the radiator.  This fits with the above description as
    far as the operation of the clutch fan.

    If this indeed is how they work then I am confused.  Why would the fan
    be making so much noise, operating at full rpm apparently, when the
    engine is cold?  Wouldn't the control mechanism have the clutch in
    primarily the free-wheeling mode when the engine is cold?  One day this
    week at lunch a buddy and I went out into the parking lot.  We opened
    the hood and he watched and listened as I started the engine.  I then
    walked around to the front of the vehicle and the noise was not too
    loud.  Suddenly, the fan noise increased dramatically and stayed that
    way.  I wouldn't expect the temperature to be sufficient to cause the
    fan clutch to fully engage under these conditions.  Maybe I'm missing
    something.

    Ron

    ref. .5
    
    Yep, you're missing something... the engine may idle at say 700rpm,
    but the fan/water pump has a smaller than engine crank pulley, by 
    maybe 1/3 to 1/2 which means the fan rpm will be 1/3 to 1/2 X FASTER
    spinning than the engine rpm.  
    
    Also, a high pitched fan is noiser than a shallow pitched fan.  The
    difference between say, 400 rpm and 2200 rpm will be significant
    in terms of noise.  
    
    A radical but valid comparison would be between the noise a turbo-prop
    plane makes with the props spinning while taxiing and the dramatic
    change in noise when it is taking off.  They INCREASE the pitch of the
    props so they pull more air and move the plane.  Once they are cruising,
    they back off of the pitch to give quieter operation, yet the engines are
    driving the props at EXACTLY the same rpm.
    
    In this example, they are changing the PITCH instead of the rpm.  In
    the car's case, they are changing the rpm instead of pitch... either
    case, same effect... more or less air being pulled, and pulling a 
    LOT of air is a NOISY proposition. 
    
    O.K.?  Didn't lose you? 
    
    J-

    ref. .6
    
    I think you missed Ron's point. He's wondering why his fan is running
    at full speed (fully engaged clutch) when the engine is cold, not why
    the fan is so loud at full speed. Maybe the thermostatic switch that
    controls the fan clutch is bad.

>                    <<< Note 1638.6 by BRAT::J_GALLAGHER >>>
>                 -< Lots o'air being pulled = lots o'noise... >-

>    Also, a high pitched fan is noiser than a shallow pitched fan.  The
>    difference between say, 400 rpm and 2200 rpm will be significant
>    in terms of noise.

    OK, I don't have any problem understanding that.

    However, I still am confused about this.  Let me provide an additional
    example.

    Yesterday morning my wife and I went out early in the morning.  As I
    backed out of the driveway (uphill to the street) the fan was making
    tons of noise.  As I drove away from the house, the noise continued and
    this went on for several miles before finally quieting down.

    This morning I left for work, backed out of the drive same as yesterday
    except that there was no noise from the fan, only the engine revving.
    I drove all the way to work with no "abnormal" fan noise.

    Other than the outside temperature being lower today - 40s as opposed
    to 50s - everything was pretty much the same.  Why is it noisy one time
    and not the other?

    I think I'm going to call the service technician at the dealer and talk
    to him a little more about this.

    Ron

My fan clutch died and was replaced several times on my old Jeep Wagoneer;  I
got quite deft at replacing it until I decided to spring for a $65 clutch at
NAPA rather than the $35 clutches at Checker.  Never had another problem after I
installed the NAPA one.

Symptoms sound the same; it roared almost all the time.  I'd replace the fan
clutch, bet'll fix your problem.

                           Roak

Ps.  I had one failure that was intermittent, it also sounds like you described
in -.1.  Sometimes it roared, sometimes not.

PPs.  I was able to fix the problem temporarily (very temporarily) by dousing
with WD40 the clutch, shaft and every nook and cranny in the clutch that looked
like it might let some lubricant inside.  Fixed it for a week or two, then I
replaced it.

    ref .7
    
    I'm afraid you both missed my statement that that's the way they are 
    SUPPOSED to behav...
    
    There's nothing defective with a fan clutch that acts like it's in
    lockup when cold/cool.  They're defective if they NEVER run fast (i.e.
    "loud"), which means either the lockup clutch is shot or the fluid has
    all leaked out. 
    
    They ALL run full lockup when "cold" for the following reasons:
    
    1. IN COLD WEATHER, fluid thickens up and tends to require some 
       warming up to thin it out well enought to allow freewheeling. 
    2. IN HOT WEATHER, if the car is used for, say, short hops, shopping
       etc. and parked warm, the ENTIRE clutch assembly gets hot from the
       residual engine and radiator heat that builds up when the engine is
       shut off.  You see, even though the engine has been shut off, 
       it's STILL HOT plus the circulation of coolant and air through the 
       engine, radiator, and engine bay has suddlenly stopped... the heat
       from the hot engine has nowhere to go, so it all just sits there and
       cooks for a while.  Volkswagen are one of the few carmakers whose
       electric cooling fans will run even after the ignition is shut
       off... primarily to prevent boilover and stress on gaskets and the 
       cylinder head.  
       
       Anyway, the clutch activating thermostatic spring gets heated up along
       with the rest of it and puts the fan clutch in the lockup mode until
       the engine is re-started and the fan can pull enough cool air through
       the radiator to cool everything down under the hood.  When it does, 
       the spring will retract and disengage the lockup clutch.  
    
    So, which words or syllables of my statement, "Operating Normally", did 
    someone not understand?
    
    Regards,
    
    J-

    I have to agree with the reply which said he went to NAPA and bought a 
    "QUALITY" unit...
    
    The manufacturers actually `price spec.' parts; i.e., they
    tell the vendors to shave this/that quality tightness, thickness, 
    longevity etc. in order to save as little as fractions of a cent on a
    per part price.  In this particular case and in the case of items like 
    brakes, shocks, tires etc. the aftermarket parts are usually superior 
    to the standard (not heavy duty) quality factory ones.  Fan clutches from
    "Hayden", York, TRW etc. are ALL superior to the factory
    `price-spec'ed ones. 
    
     There's also a point that might be overlooked here... Blazers etc.
    are built upon TRUCK running gear mostly... that includes "BUS" fans.
    They are passenger vehicles, but they are built for more abuse than
    your father's Oldsmobile.  If one wants quiet, then why buy a truck?
    
    I too had some problems making the transition from car to truck about
    1-1/2 years ago... except mine had a high pitch fan with NO clutch...
    which sounded like a "BUS" full time!  I put a clutch in... now it's 
    only noisy PART TIME which I can live with. 
    
    If you truly can't live with normally noisy truck cooling systems...
    have an electric fan setup installed... it is mounted on the front
    of the radiator/condensor and it's output is silenced by both cooling
    cores.
    
    J-
    

>                    <<< Note 1638.11 by BRAT::J_GALLAGHER >>>
>                   -< It's a TRUCK more than it's a CAR... >-

    J-,

    Thanks for all the feedback.  It is appreciated.

    I spoke with my service technician and he said he is willing for me to
    come in and have someone take a close look at it to see if perhaps it
    is performing out of spec.  I'll set that up soon and report back.

>    There's also a point that might be overlooked here... Blazers etc.
>    are built upon TRUCK running gear mostly... that includes "BUS" fans.
>    They are passenger vehicles, but they are built for more abuse than
>    your father's Oldsmobile.  If one wants quiet, then why buy a truck?

    I agree with this statement to a point.  True, Blazers are built upon
    truck running gear.  By the way, just in case this isn't clear, I am
    talking about the Blazer (formerly known as the S-Blazer) and not the
    Tahoe (formerly known as the Blazer).  Anyway, the typical buyer of any
    of today's SUVs is not someone who is looking for a truck-like vehicle.
    Most of these vehicles will never even see a dirt road, never mind do
    any serious (or semi-serious) off-roading.  I think most customer's
    expectations in an SUV are for a comfortable vehicle with the
    additional security of 4WD.  After all, look at the interior of the top
    of the line models!  Heck, just about every car maker out there is
    jumping on the SUV bandwagon.
    
>    If you truly can't live with normally noisy truck cooling systems...
>    have an electric fan setup installed... it is mounted on the front
>    of the radiator/condensor and it's output is silenced by both cooling
>    cores.

    This is something that might be considered in the future.  However,
    since this thing is still under warranty, and will be for a while, I
    don't want to change any component that might have GM pointing at later
    as the cause of some failure.

    Ron

    Ron,
    
     I agree.  You should try to seek satisfaction under warranty until the
    vehicle suits you or they've run out of honest attempts or you run out 
    of patience and money.  
    
    There's literally no reason they couldn't have put an electric fan setup
    in that particular vehicle...the more rugged mechanical design is
    simply a carryover from it's light truck bloodline and probably isn't 
    necessary in well over 90% of the units sold.
    
    Regardless of what consumer's expectations are, the American-built 
    SUV's are built on light truck-duty chassis and running gear... just 
    the way it is.
    
    It's a paradox, actually... the SUV's have progressively been getting
    puffed up with luxurious interiors, appointments and options, but when
    you start adding 4X4, rugged tread tires, heavy duty towing pkgs.,stiff 
    springs, shocks etc... they become stiff and noisy compared to a CAR, 
    (which they're NOT). 
    
     It's kinda sad, really.  Folks are paying some pretty high prices for
    vehicles they expect to act like cars with 4WD.  SOMETHING had to
    replace the family station-wagon, and SUV's are a logical evolution;
    but if you want REALLY luxurious, quiet and smooth 4X4's you either 
    have to get SUV's built from the ground-up on car type running gear
    (Mercury Mountaineer comes to mind.. sort of car, minivan and SUV all 
    at once), or one of the waaayyyy over the top luxury SUV's like the big
    Land Rovers or Lexus's, or the more sleek Audi, BMW, Mercedes
    "quadra-trac" type luxury cars... That is if you care to spend an extra
    $10-15K for not much else than a name.   They're GREAT vehicles, actually,
    but costly to buy, costly to maintain, and depreciate like a 1 week old 
    pizza.  It becomes irrelevant whether they last any longer, perform better
    or take any more abuse than a Blazer, Explorer etc.; a bad investment, 
    (er, unnecessary EXPENDITURE), is a bad investment. 
    
    As for the "extra security of 4X4", most folks have very little
    understanding of the limitations of an SUV in terms of handling and 
    stopping and somehow are lulled into a false sense of security about
    what "4X4" actually does for a vehicle.  Primarily, it's a `launching'
    mechanism used at low speeds only, to get the vehicle going in poor
    traction conditions...that's about it.  We're not talking the `out
    back' or `sporting' uses for 4X4... just street use.
    
    Most SUV's are actually more dangerous on icy or snow covered smooth 
    surfaces than the average mid to full size front wheel drive sedans on 
    the road today.  It has more to do with the vehicle's physics, not 
    "4X4-ness".  (see discourse in Dodge Durango notes). 
    
    Good luck with your dealer...
    
    Regards,
    
    John

Re: <<< Note 1638.13 by BRAT::J_GALLAGHER >>>

>>    ...what "4X4" actually does for a vehicle.  Primarily, it's a `launching'
>>    mechanism used at low speeds only, to get the vehicle going in poor
>>    traction conditions...that's about it.

Reminds me of a favorite saying of mine (for street use of 4wd):

   Four wheel drive will get you in trouble faster than two wheel drive.

I've got a friend with a similar saying (for off road use of 4wd):

   Four wheel drive will get you stuck in better scenery.

                          Roak :-)

    RE .14
    
    Ayuuh, that's about the best summary of 4WD I've ever seen... not exactly
    the kinda info. the vehicle VENDORS will freely share with you, for sure.
    If they did, they wouldn't sell very many, would they?
    
    You're absolutely right!  "4WD SUV" means you can get into DEEPER trouble
    FASTER than in a car which very QUICKLY warns you that you've crossed
    over the line between safe operation and the Twilight Zone.
    
    A friend of mine with an Explorer told me one morning that the previous
    evening he was bombing down the highway about 65 in a snowstorm in 
    "4WD".  Before he could do ANYTHING about it, a sudden a wind gust
    caused him to do two complete 360's .  He felt lucky no other vehicles
    were close to him or that he didn't leave the road.
    
    I asked what made him think that pushing a button or shifting a lever
    magically changed his vehicle' center of gravity, profile to the wind,
    tires, suspension, brakes etc.?
    
    DUUHHH!

>       <<< Note 1638.12 by SSDEVO::THELLEN "Ron Thellen, DTN 522-2952" >>>

>    I spoke with my service technician and he said he is willing for me to
>    come in and have someone take a close look at it to see if perhaps it
>    is performing out of spec.  I'll set that up soon and report back.

    I left the Blazer at the dealer yesterday.  The results were...

    "We drove it around the block and heard the fan noise.  Then we took
    another '97 from the lot and drove it and heard the same noise.  Normal
    operation."

    So much for taking a close look!

    This week it has actually been fairly quiet so I'm not sure they
    actually heard the sound level that I have experienced on occasion.

    Any idea on where I could find out detailed specs on the operation of
    the fan clutch, e.g., designed temperature at which the clutch
    operation kicks in?  I'd like to compare that to specs on aftermarket
    units to see if it might be worth my effort to consider replacing it.

    Ron

    Ron,
    
    There are different specs for different vehicles.  The clutches are 
    spec'ed to operate within certain rpm ranges and be sensitive to
    certain temperature ranges (cut-in/out).  There's literally nothing
    you can do about thick fluid in the Winter till the clutch loosens
    up, and literally nothing you can do about hot restart when the clutch
    thermo-spring has been exposed to a hot radiator and is mounted to a 
    hot (aka boiling) block.  The fan's gonna run full tilt in either
    situation, both of which are upon startup.
    
    Quieter operation lately is probably due to the increasing warmness of 
    ambient temps (the warm months).
    
    I'd go for a heavy duty setup (clutch and fan) off a full sized CAR
    with all the toys, like a RWD Chev Caprice... it should be a direct 4
    bolt exchange and run one helluva lot quieter. 
    
    Although they've come a looooong way in the last 7-8 years, 
    quiet simply isn't as important as heavy duty is with truck drivelines.
    
    A boneyard will actually remove the assembly along with bolts spacers
    etc. FOR you so that all you have to do is go get it over the counter
    at something like 1/4 what a new one would cost.
    
    Good hunting. 
    
      John