Fixed Flex Fan - Complete DIY Part Number List

Fulltimer · **Posted:** Wed Apr 07, 2010 12:30 am

When you get old you get shorter. The Appalachian mountains are much older than the Rockies. But anyway, who cares about it? It's off topic.

Terry

emp1134 · **Posted:** Wed Apr 07, 2010 3:36 am

don't know if there is enough room for it or if there is smaller fan to fit it, but the 3rd gen(03-09) Dodge with the Cummins use an electric controlled fan clutch.

europachris · **Posted:** Wed Apr 07, 2010 7:31 am

onthehunt wrote:

They are air controlled. Not really an option. They work the same way as a viscous clutch. The only benefit is longer lasting and rebuildable. I can't see gaining anything with a flex fan. Nice work though. Not trying to rain on your parade.

Thanks for the clarification! I wasn't positive on the method of actuation, but air certainly makes more sense in a large truck.

LOL, I wonder if we could adapt an electric PTO clutch from a lawn tractor for the job.....the one on my Cub Cadet 2544 sits right out in front on the horizontal shaft of the Kohler, and the only difference is it has a pulley on the end of it rather than a fan. Only issue is the PTO clutches have been known to grenade (Cub is cheap like Chrysler), and the engagement is very abrupt - pretty much ON or OFF, but I imagine that could be worked around....

ATXKJ · **Posted:** Wed Apr 07, 2010 7:48 am

The only time my temp gauge has ever gotten over 1/2 way - was climbing I 70 coming out of Denver - and the Engine rpm was in the 3000+ range - so a Flex fan would not have done any good. (not sure if the clutch engaged - I pulled off and let things cool down)

running around Austin in 100+ temps with the AC on - the temp gauge never went over 1/2.

so it's not clear to me that a flex fan would be pulling air when needed i.e. high engine speed - low Jeep speed.

LibertyCRD · **Posted:** Wed Apr 07, 2010 10:10 am

What diff. does it make if a mountain range is 20,000 ft. or 6,000 ft.?? The higher elevation you go, the cooler the ambient temp. gets anyway.. Point is...a steep grade is a steep grade, and if the CRD can tackle steep mountain grades in 91 degree weather loaded with 5 people and gear and not even go past the half way mark...then it's good to go without the clutch fan.

UFO · **Posted:** Wed Apr 07, 2010 10:47 am

Sounds like an excellent idea to replace an unreliable component. I take it the "Imperial" brand part is the same diameter as the original?

JL Rockies · **Posted:** Wed Apr 07, 2010 2:25 pm

LibertyCRD wrote:

What diff. does it make if a mountain range is 20,000 ft. or 6,000 ft.?? The higher elevation you go, the cooler the ambient temp. gets anyway.. Point is...a steep grade is a steep grade, and if the CRD can tackle steep mountain grades in 91 degree weather loaded with 5 people and gear and not even go past the half way mark...then it's good to go without the clutch fan.

It's not the steep, it's the length that gets ya. And as the air gets thinner, the fans become less effective.

We had a few heat problems at 12K ft in Ouray last July. I even had a trans temp warning because I frogot to put 'er in 4LO.

JL Rockies · **Posted:** Wed Apr 07, 2010 2:34 pm

And Teh Rockies is teh ownz.

Goglio704 · **Posted:** Wed Apr 07, 2010 3:22 pm

I wonder if the nice lady from the movie Airplane is still around to translate?

Goglio704 · **Posted:** Wed Apr 07, 2010 3:26 pm

Hats off to both experimenters in this thread. Please keep us informed about the good and bad of both approaches.

Squeeto · **Posted:** Wed Apr 07, 2010 4:36 pm

Any one have a better trick to test a viscous fan clutch than purposely overheating your engine?
Maybe carefully with a torch?

Goglio704 · **Posted:** Wed Apr 07, 2010 5:11 pm

You'd have to be careful with a torch. Maybe a heat gun would be better?

geordi · **Posted:** Wed Apr 07, 2010 5:51 pm

Just a thought, but try this: Take it off the engine, put it in an oven at 250 or so and let it heat-soak for a good bit. Then take it out and see if the shaft is locked to the fins by trying to rotate it.

Slow heating like in an engine, not point-heating with a heat gun or torch is what you are looking for.

Goglio704 · **Posted:** Wed Apr 07, 2010 6:07 pm

Just make sure it is kept vertical. If laid flat, the fluid can migrate to places it wouldn't normally be.

kapalczynski · **Posted:** Wed Apr 07, 2010 6:59 pm

Wow, a lot of questions and ideas on the forum in just a day!

I'll answer everyone individually if I can keep up with you all.

europachris wrote:

What makes the CRD fan clutch more prone to fail than any other application? Crappy Chrysler part to begin with? :BINGO:

Viscous fan clutches have been around a long time, but frankly, I don't see how they ever actually work properly or reliably - that's just the engineer in me talking.

What we REALLY need is an electric fan clutch like the Class 8 highway tractors use, and you could even put in a manual override switch to cut out the fan for a momentary "boost" for passing, etc. Otherwise, the fan would be thermostatically controlled just like a front wheel drive car except the engine would provide the fan power rather than an electric motor. You could even combine the fan clutch with a flex fan for the best of both worlds.

Chris

All good ideas...

Here's my thoughts:

"Fan clutch prone to fail" -
Just based on all the members on here that have had problems

"more than any other applications" -
I can't vouch for other applications, but is most cases (and this is only according to wikepedia) the viscous fan clutch is considered "reliable" and that is why OEM's use them. Of course how "reliable" is wikepedia itself anyway? lol

"Electric fan clutch" -
Why not just dual electric fan's at that point...they would come on at 2 different temps like most other modern cars. Only consumes power when needed, which would be rare most likely on our jeeps. Even with electric the car provides the power through the alternator which also loads the engine. In my opinion, much more efficient than a clutch setup though.

"fan clutch with a flex fan for the best of both worlds" -
This WOULD be a good idea, except I already looked for flex fans that fit our application...are none. It would also COMPLETELY negate the fact that we have to replace our $142.00 fan clutch every ~50k miles. This is a solution for far superior cooling compared to stock and unlimited reliability at 2/3's the cost of the fan clutch alone.

- Mark

kapalczynski · **Posted:** Wed Apr 07, 2010 7:02 pm

JL Rockies wrote:

6000 ft is the bunny trail yo.

My house is at more than 6000ft. I drive up to nearly 12k feet on the weekends several times a summer...quite a few times in the winter too now that I think of it.

kapalczynski · **Posted:** Wed Apr 07, 2010 7:04 pm

emp1134 wrote:

don't know if there is enough room for it or if there is smaller fan to fit it, but the 3rd gen(03-09) Dodge with the Cummins use an electric controlled fan clutch.

Might be worth looking into if it is more reliable. Although, I'm sure its even more $$$ than ours and possibly more weight too with the electric clutch.

kapalczynski · **Posted:** Wed Apr 07, 2010 7:14 pm

ATXKJ wrote:

The only time my temp gauge has ever gotten over 1/2 way - was climbing I 70 coming out of Denver - and the Engine rpm was in the 3000+ range - so a Flex fan would not have done any good. (not sure if the clutch engaged - I pulled off and let things cool down)

running around Austin in 100+ temps with the AC on - the temp gauge never went over 1/2.

so it's not clear to me that a flex fan would be pulling air when needed i.e. high engine speed - low Jeep speed.

"gotten over 1/2 way" -
I wouldn't doubt if your fan clutch is bad if you hit that temp. I would use the Proper test procedures to check it if I were you. I'll post procedures in a few, it is an easy test that requires virtually no tools.

"and the Engine rpm was in the 3000+ range - so a Flex fan would not have done any good" -
Actually it would have helped SIGNIFICANTLY at those RPM's It doesn't even START flexing till about 3k RPM's and the 6 curved blades move A LOT more air even partially flexed at 4k RPM's than a factory 5 blade fan w/ clutch locked(though I'm betting yours wasn't).

I highly HIGHLY doubt your temp gauge would ever spike over half with a solid linked flex fan even pulling a 5k+ pound trailer up a mountain.

kapalczynski · **Posted:** Wed Apr 07, 2010 7:18 pm

UFO wrote:

Sounds like an excellent idea to replace an unreliable component.

My thoughts exactly

UFO wrote:

I take it the "Imperial" brand part is the same diameter as the original?

Actually 1/4" larger radius and 6 curved blades instead of 5 flat, but still plenty of room in the shroud for engine movement bouncing over rocks and revving up. Pushes a lot more air.

kapalczynski · **Posted:** Wed Apr 07, 2010 7:37 pm

Squeeto wrote:

Any one have a better trick to test a viscous fan clutch than purposely overheating your engine?
Maybe carefully with a torch?

There is a really simple test where all you need is a piece of cardboard and your jeep:

Block the radiator with a piece of cardboard, hold the engine at 2400 rpms until you hit at least 195*-205* F (lock up temperature), shortly after hitting 200* F you should hear the fan engaging with more air flow and it should get loud. This is not bad for your jeep as long as you do not exceed 225* F (roughly 5/8 on the gauge) when the fuel starts to cutoff to safe the engine (See Image below from GDE). Clutch should dinengage somewhere between 145*-185* F. Try it out and see if your fan clutch is still good!

According to the manual:

"RADIATOR - FAN - VISCOUS
DESCRIPTION
CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected. Inspect for
fatigue cracks, loose blades, or loose rivets that
could have resulted from excessive vibration.
Replace fan blade assembly if any of these conditions
are found. Also inspect water pump bearing
and shaft assembly for any related damage due to
a viscous fan drive malfunction.
The thermal viscous fan drive (1) is a silicone-fluidfilled
coupling used to connect the fan blades to the
water pump shaft. The coupling allows the fan to be
driven in a normal manner. This is done at low engine
speeds while limiting the top speed of the fan to a predetermined
maximum level at higher engine speeds.
On the 3.7L engine, an electric fan is standard and the viscous fan is added on for trailer tow packages only.
On the 2.8L diesel engine, the viscous is standard.
OPERATION
A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. This spring coil reacts
to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air
temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will
remain at a reduced rpm regardless of engine speed. Normally less than 800 rpm.
Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the
radiator core causes a reaction to the bimetallic coil. It then increases fan speed to provide the necessary additional
engine cooling.
Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the
fan speed is reduced to the previous disengaged speed.
DIAGNOSIS AND TESTING
VISCOUS FAN DRIVE
If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand),
replace the fan drive. This spin test must be performed when the engine is cool.
For the following test, the cooling system must be in good condition. It also will ensure against excessively high
coolant temperature.
WARNING: BE SURE THAT THERE IS ADEQUATE FAN BLADE CLEARANCE BEFORE DRILLING.
1. Drill a 3.18-mm (1/8-in) diameter hole in the top center of the fan shroud.
2. Obtain a dial thermometer with an 8 inch stem (or equivalent). It should have a range of -18° to 105°C (0° to
220° F). Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the
fan blades.
3. Connect a tachometer and an engine ignition timing light (timing light is to be used as a strobe light).
4. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser).
Use tape at the top to secure the plastic and be sure that the air flow is blocked.
5. Be sure that the air conditioner (if equipped) is turned off.
KJ ENGINE 7 - 61
WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE
WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE
CLOTHING.
6. Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial thermometer)
should be up to 93° C (200° F). Fan drive engagement should have started to occur at between 91°
to 96° C (195° to 205° F). Engagement is distinguishable by a definite increase in fan flow noise (roaring). The
timing light also will indicate an increase in the speed of the fan.
7. When the air temperature reaches 93° C (200° F), remove the plastic sheet. Fan drive disengagement should
have started to occur at between 62° to 85° C (145° to 185° F). A definite decrease of fan flow noise (roaring)
should be noticed. If not, replace the defective viscous fan drive unit."

Fixed Flex Fan - Complete DIY Part Number List

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