Is it safe to run the fan clutch thermal fan on an engine that red lines at 6,000 RPM's? I noticed on the Hayden web page that the fans are rated at 4,000 RPM's. Surely these fans are ran on high performance engines with red lines between 5,500 and 5,800 RPM's.

Trust Ma. She knew. Never had a problem w/thermal at any RPM.

No flex. No electric. No aluminum.

I run a thermal fan clutch on a 6000 RPM application and they are in common use on street/strip combos at 6500 and beyond. Apparantly the thermal clutch slips enough at high RPM to keep fan speed reasonable. I'm sure they are not all the same though.

I use the MP thermal fan kit. My one experience with aftermarket on a newer Durango wasn't good and I went back to a MOPAR clutch. The "torqflow" unit was spinning the fan at high speed in very cold temps.

Bottom line I wouldn't have any concern running the MP setup on a 6500 RMP application

John Heywood's 1988 book on
Internal Combustion Engine Fundamentals
gives this interesting graph of
the power consumed by engine accessories like
solid fans, viscous clutch fans, power steering pumps and generators.
Note that the left scale is kilowatts,
not SAE HP.

At least for the viscous clutch fan
they tested it to 6000 rpm,
but for some reason they stopped short
on the solid fan maximum rpm.

Of the two references cited,
one is for the
1968 SAE paper Number 680019
about the Chrysler 340 V8 engine.
http://papers.sae.org/680019

on another point
look how in the lower rpms
the solid fan
actually consumes a little less HP
than the viscous clutch fan,
although we can't be certain
the two fans have exactly the same blades

Let me clarify. When the engine gets hot the thermal fan clutch spring tightens making the fan turn faster. It kind of "locks up" so to speak. That will make the fan spin much faster especially at higher engine RPM's. So, what all of you are saying is even if the thermal clutch spring gets tighter, making the fan spin faster, it still won't spin fast enough to fly apart with the engine turning 6,000 RPM's?

In a 10 to 15 second quarter-mile run,
when the vehicle speed is 20 to +90 mph
it is unlikely that even at full throttle output,
will the air going by the radiator
and hitting the viscous clutch bi-metallic spring
get hot enough quickly enough to lock it during the short run.

When you let off the throttle
and the vehicle slows down to 5-10 mph
for the return to the pits
then the delayed heat in the radiator will flow past the bi-metallic spring
and it will probably lock up the clutch
but the engine rpms will be low.

The horsepower a fan requires goes up so dramatically with rpm,
that there will be a rpm limit
at which it flies apart.

Yesterday I destroyed the little plastic propeller
in an $20 Eddie Bauer 'Weather Watcher' wind speed meter,
when I pressed it up against the nozzle of a wet-dry vacuum.
The wind speed went whizzing up to 100 mph on the digital display with a roaring noise,
... then 'Pop'
and the axle of the fan broke,
and now the little meter is only good for measuring air temperature.



I guess I will now have to spend $64
and buy a
Brunton ADC Summit wind speed meter,
but it might be a good upgrade
because it can also measure water speed
if you are in a kayak or canoe,
or want to measure the water coming out of
a large pipe.

http://www.amazon.com/Brunton-ADC-Wind-M...mp;sr=8-1-fkmr2

You can use these inexpensive wind speed meters
to approximately answer the frequent forum question:
How many CFM does my radiator fan actually pull?

I have fan clutch on my 408 and have been shifting it at 6500 for the last four years with no problem. It has seen 7500rpm at times.

Maybe I'm over thinking this. But...if the water temp is already at 210 degrees, the thermal spring has tightened up spinning the fan much faster, will it be spinning so fast at the engine's 6,000 RPM's that it will come apart? Or...will the thermal fan clutch never fully "lock up" no matter how hot the water temp gets?

I'm only talking about thermal fan clutches with the bimetal spring. I'm not trying to be an [Edited by Moparts - Family Friendly Site - Keep it clean] here, just trying to understand.

I feel stupid trying to get this clarified.

Even though its "much faster" its still slipping. At 6k with a MP clutch and fan I wouldn't sweat it at all. With another brand clutch and fan... ?

you should contact haydens tech dept. i had the same concern after i saw the warning on the hayden fan. they told me that they do not recommend their fan at that rpm even with a clutch. find a good used original one.

all fan clutches, thermal and otherwise, slip at high speed. because of that, you won't find a fan clutch fan rated for high rpm- it's not necessary. flex fans are direct drive (obviously), therefore they're almost all rated for at least 8000 rpm (sometimes 10000).

say no to flex fans!!

what flattens them out? drag and air resistance!

what's that mean? it's loading down your engine and sucking up unneeded HP. at that RPM, hopefully you're moving fast enough that you don't NEED a fan to pass air through the radiator!

clutch fan or electric fan. no flex fans!

I have a ginormous 19" eletric fan that I can force it off until my big block would hit 225, and even in 90 degree weather, sitting idling with no air movement, the fan would bring me back down to the thermostat setting of 160 in just a few minutes.

and at max draw, that fan would only pull 30 amps, maybe 20 at steady run speed. that's more than enough for even the "wimpy" stock alternators to keep up with unless you're talking about a street car with electric fan, electric water pump, huge stereo and amps, AC with the blower set on high, etc. --but in that case...you should upgrade your alternator anyway if you're running a stereo, A/C, etc.

i used to advise against flex fans (i'm in the cooling business), but after first hand experimentation on my very own "mule" ( under the most adverse conditions imaginable), i changed my opinion about them. they work GREAT. they might be a problem cruising through town at 6000 rpm in low gear, but a good flex fan (like a flex-a-lite or something similar) works extremely well. i think flex fans got a bad rap because of some crappy ones out there.