Explanation needed of Mercury Marquis cooling fan clutch operation

My Mom has a 1995 Mercury Grand Marquis with a radiator/engine
overheating problem. The temperature skyrockets on occasion during
slow, stop/go driving. Upon stopping and opening the hood with the
engine still running, I see that the water pump belt-driven cooling fan
is not turning(the smaller aux electric fan is running[while AC is on])
and the belt is not slipping.

I've been told my various shade tree mechanics that there is a clutch
that gets the fan blade turning, but as to how the clutch is activated,
I get varying stories. Some say the clutch is centrifugally activated
due to the RPM of the drive belt. Some say the clutch is electrically
activated by a fan clutch switch but the location of said switch is not
known...some say in the radiator, some say in the thermostat, some say
in the engine block.

If there is a switch, I'm thinking it's thermostatically activated, but
that's a guess on my part. That stuff about centrifugal activation
kind of has me puzzled.

I'm used to GM vehicles' electric cooling fans, having had to replace
one on a Celebrity, and two on a Century. Voltage present to fan, but
fan doesn't work...bad motor. No voltage to fan motor, switch problem.
Simple.

I'd appreciate a "How it Works" tutorial on a, for lack of a better
name, mechanical cooling fan. Thanks for any information or insight
you can provide. Also, if you know whether it's the clutch or switch
that is the more common culprit.

Danny getting hot in Yorktown, VA

"Danny" > wrote in message
oups.com...
> My Mom has a 1995 Mercury Grand Marquis with a radiator/engine
> overheating problem. The temperature skyrockets on occasion during
> slow, stop/go driving. Upon stopping and opening the hood with the
> engine still running, I see that the water pump belt-driven cooling fan
> is not turning(the smaller aux electric fan is running[while AC is on])
> and the belt is not slipping.
>
> I've been told my various shade tree mechanics that there is a clutch
> that gets the fan blade turning, but as to how the clutch is activated,
> I get varying stories. Some say the clutch is centrifugally activated
> due to the RPM of the drive belt. Some say the clutch is electrically
> activated by a fan clutch switch but the location of said switch is not
> known...some say in the radiator, some say in the thermostat, some say
> in the engine block.
>
> If there is a switch, I'm thinking it's thermostatically activated, but
> that's a guess on my part. That stuff about centrifugal activation
> kind of has me puzzled.
>
> I'm used to GM vehicles' electric cooling fans, having had to replace
> one on a Celebrity, and two on a Century. Voltage present to fan, but
> fan doesn't work...bad motor. No voltage to fan motor, switch problem.
> Simple.
>
> I'd appreciate a "How it Works" tutorial on a, for lack of a better
> name, mechanical cooling fan. Thanks for any information or insight
> you can provide. Also, if you know whether it's the clutch or switch
> that is the more common culprit.
>
> Danny getting hot in Yorktown, VA
>

The engine driven fan is equipped with a viscous clutch. It operates by
allowing the fan to spin more freely( slip) when the clutch hub is cool,
but as the hub gets heated up by the hot air flowing through the cooling
radiator it begins to grip more completely and does not allow as much
slipping of the fan on the hub. Inside the fan clutch are some metal clutch
plates immersed in a viscous silicone material. That material gets thicker
as it gets hotter and the thicker fluid causes more friction between the fan
clutch plates. When it is fully warmed up we say it is engaged because very
little slippage is occurring between the engine pulley and the fan blades.
Some types of fan clutches also have an internal spring that uncoils as it
gets hotter. This spring applies more pressure to the clutch discs and
causes them to have more friction. Either way, there is no electrical switch
or thermostat so to speak, that is used. The fan clutch is a sealed unit and
is replaced whenever it fails to perform as required.
To check it for proper operation, you should warm the engine up to normal
operating temperature then have an assistant turn off the ignition while you
watch the fan. If the fan continues to spin for more than one second after
the engine stops then it needs to be replaced.

Some more information on cooling fans he
http://www.cdxetextbook.com/engines/...ght=fan+clutch

hope this helps.

--
Kevin Mouton
Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green

As Kevin has posted, those hubs work to increase viscoelastic coupling as
the
temperature increases so that the fan rotates faster at higher temperatures
than they
do when the engine is cold. If you had a direct drive fan (which cars used
to have)
they would always run at full speed, increasing noise and draining
horsepower.
(A fan can easily consume 2-3 horsepower)

If this fan isn't turning adequately with the engine hot, then the engine is
likely
to overheat when you are driving at low speed. At highway speed you may get
enough air flow that it will not overheat, but the problem will be back
again as
soon as you slow down.

Now, what do you do about it:
(1) Replace the viscous hub with an aftermarket or dealership one
(2) Replace the whole mess with a 'flex fan'. (I prefer the stainless steel
ones)

Both, IMHO, are good options. One may be substantially cheaper than the
other.

"Danny" > wrote in message
oups.com...

> I've been told my various shade tree mechanics that ------

Just one other little word of counsel...You will hear a lot of things from
people, many of which seem to make sense, but which may not be totally
correct.

Automobile systems are more complicated now than they have ever
been before, and a good mechanic needs to be current with the actual
theory and facts about how systems work before he (or she) can troubleshoot
them properly.

The more you learn about how the car works, the more you can do for
yourself,
and the more you can avoid bad advice. Dealership mechanics can be just as
guilty at putting out misinformation as others.

Learn how things work, and you will save yourself time, heartache, and LOTS
of money.

Kevin and HLS, thanks for the information and description of how a
viscous hub clutch works. HLS, could you give me some more information
on a "flex fan." I can't find a lot of information on it, other than a
company called flex-a-lite, and I'm not sure that they carry what
you're talking about. I've found several references to a Hayden HY2795
as a suitable replacement for a 1995 Grand Marquis as far as viscous
hub clutches.

Thanks again.

Getting cooler in Yorktown, VA...Danny

The saga continues on my Mom's 1995 Mercury Grand Marquis with an
overheating problem. I had the viscous hub fan clutch assembly
replaced since it would barely turn with the car at and above normal
operating temps. The new viscous hub fan clutch is now doing the same
thing as the old one(and I know there is a new one in place as the
mechanic, a friend who I trust, showed me the old one). When I drove
the car home(roughly 8 miles in stop and go traffic) the temperature
gauge was within 15 degrees of the top of the scale. Once in my Mom's
drive way, I opened the hood and there was the radiator cooling fan
spinning at 25 rpm or so...so slow I could make out each blade
distinctly. I cut the engine off and then restarted. From inside the
car, I could see the top of the fan blades inside the open hood and saw
them take off at a blur. After 15-30 seconds, the fan slowed down to
the previously mentioned ineffective speed. I turned the car off and
restarted once again. This time the fan started up at high speed and
ran at high speed for the next ten minutes until the temperature
indicator had dropped down to the 190-200 degree level and I turned the
car off.

Any suggestions?

It may have been an optical illusion, but it seemed that the fan shaft
just beyond the water pump belt hub was not moving very fast either.
Is there another clutch where the water pump belt rides on the bulbous
hub/base(just outside the engine block)? The belt does not appear to
be slipping. Is there any reason that the water pump belt would be
operating at a slower rpm than the engine's rpm?

Thanks for any advice/suggestions.

Danny in Yorktown, VA

"Danny" > wrote in message
oups.com...
> The saga continues on my Mom's 1995 Mercury Grand Marquis with an
> overheating problem. I had the viscous hub fan clutch assembly
> replaced since it would barely turn with the car at and above normal
> operating temps. The new viscous hub fan clutch is now doing the same
> thing as the old one(and I know there is a new one in place as the
> mechanic, a friend who I trust, showed me the old one). When I drove
> the car home(roughly 8 miles in stop and go traffic) the temperature
> gauge was within 15 degrees of the top of the scale. Once in my Mom's
> drive way, I opened the hood and there was the radiator cooling fan
> spinning at 25 rpm or so...so slow I could make out each blade
> distinctly. I cut the engine off and then restarted. From inside the
> car, I could see the top of the fan blades inside the open hood and saw
> them take off at a blur. After 15-30 seconds, the fan slowed down to
> the previously mentioned ineffective speed. I turned the car off and
> restarted once again. This time the fan started up at high speed and
> ran at high speed for the next ten minutes until the temperature
> indicator had dropped down to the 190-200 degree level and I turned the
> car off.
>
> Any suggestions?
>
> It may have been an optical illusion, but it seemed that the fan shaft
> just beyond the water pump belt hub was not moving very fast either.
> Is there another clutch where the water pump belt rides on the bulbous
> hub/base(just outside the engine block)? The belt does not appear to
> be slipping. Is there any reason that the water pump belt would be
> operating at a slower rpm than the engine's rpm?
>
> Thanks for any advice/suggestions.
>
> Danny in Yorktown, VA
>

Perhaps the water pump bearings are binding and causing the belt to slip.
Although a slipping belt usually makes a squealing noise, sometimes they do
not. I would suggest removing the belt and checking all the pulleys by hand.
Spin them and feel for any roughness or play in the bearings. If everything
feels ok it may be that the new fan clutch is defective. That does happen
sometimes. Also keep in mind that the viscous clutch relies on hot air
flowing through the radiator to cause it to warm up and engage. If the
radiator fins are filled with debris and not allowing sufficient air flow,
the clutch may not get warm enough to engage when it should. Also consider
that the temperature indicator may not be reading correctly and the engine
is not actually as hot as is being indicated. Perhaps the sending unit or
the wiring or even the gage itself has a problem
--
Kevin Mouton
Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green