How to tell if fan clutch is bad? - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 01-24-2007, 03:05 PM   #1 (permalink)
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How to tell if fan clutch is bad?

How can you tell if the fan clutch is bad? Mine spins at start up but can be rotated by hand freely with engine off.
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Old 01-24-2007, 04:01 PM   #2 (permalink)
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Re: How to tell if fan clutch is bad?

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How can you tell if the fan clutch is bad? Mine spins at start up but can be rotated by hand freely with engine off.
Sounds ok to me... Does it wobble around at all ? If not then all good....
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Old 01-24-2007, 09:02 PM   #3 (permalink)
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Re: How to tell if fan clutch is bad?

It does not wobble but I run on wvo. I see oil temps about 150* on the freeway. But when idling temp drops to 110*. I think the fan is running all the time? Should the fan be able to be stoped if a wooden handle is pressed against it and the truck started briefly?
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Old 01-24-2007, 09:10 PM   #4 (permalink)
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Re: How to tell if fan clutch is bad?

when the eng. is cold & under a load, mainly on a upgrade, if you hear a loud swooshing or roaring noise, the clutch is locked up. i hav'nt seen alot of them go out though, just a few.
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Old 01-24-2007, 09:11 PM   #5 (permalink)
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Re: How to tell if fan clutch is bad?

Quote:
It does not wobble but I run on wvo. I see oil temps about 150* on the freeway. But when idling temp drops to 110*. I think the fan is running all the time? Should the fan be able to be stoped if a wooden handle is pressed against it and the truck started briefly?
The clutch fan is only supposed to work at low speed & higher temps. When moving down the road it is supposed to free wheel to keep from robbing HP. Sitting still it should always be spinning.The clutch works based on RPM's & temperature...Hope that helps....
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Old 01-24-2007, 09:18 PM   #6 (permalink)
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Re: How to tell if fan clutch is bad?

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I think the fan is running all the time?
Yes, it "runs" all the time. The fan clutch is a viscous clutch, filled with a synthetic high-viscosity oil. So even when that viscous clutch is "slipping" it's still drawing a horse or two worth of power from the engine to pull lots of air through the radiators and coolers. When it locks up under full song, it uses about 27 horses from the engine to pull a hurricane through the radiator and coolers.

Quote:
Should the fan be able to be stoped if a wooden handle is pressed against it and the truck started briefly?
I suspect that would be a very dangerous test. I wouldn't even think of trying it. Unless you can overcome about one horsepower worth of engine effort to turn that viscous clutch.

The workshop manual includes tests to determine if the fan clutch is operating properly. At the risk of boring most of the others to death, here's what it says:

Quote:
Fan Clutch Test

NOTE: The following test does not apply to the 6.0L diesel. For the 6.0L diesel, refer to the Powertrain Control / Emmisions Diagnosis (PC/ED) manual.

Spin the fan blade (8600) by hand. A light resistance should be felt. If there is no resistance or very high resistance, the minimum and maximum fan speeds must be checked as follows:

Fan Clutch Test — Minimum Speed Requirement

Use a suitable marker to mark the coolant pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
Connect a tachometer to the engine.
Install a throttle adjusting tool.
Connect the Digital Photoelectric Tachometer.
WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and run it at approximately 1,500 rpm until the normal operating temperature has been achieved.
Operate the strobe light at 3600 rpm for 7.3L diesel engines, and aim it at the coolant pump pulley. Adjust the engine speed until the light flash and the coolant pump pulley mark are synchronized.

Aim the strobe light at the fan blade bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
The fan blade speed must not be greater than 2,000 rpm on 7.3L engines.

Turn the engine off.

If the fan blade speed was greater than 2.000 rpm on 7.3L diesel engines, install a new fan clutch (8A616).

Fan Clutch Test — Maximum Speed Requirement

Perform Steps 1 through 5 of the Fan Clutch Test—Minimum Speed Requirement.

NOTE: The temperature of the air hitting the fan clutch should be above 96C (205F) for maximum fan speed.

Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200). This will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.

Place the climate control function selector switch in the MAX A/C position and the blower motor switch in the HI position.

Adjust the strobe to 3,600 rpm for 7.3L diesel engines.

WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and adjust the engine speed until the strobe light flash and the coolant pump pulley mark are synchronized.

Aim the strobe light at the fan blade retaining bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).

If the fan blade speed is less than 2,850 rpm on 7.3L engines, install a new fan clutch.
So the kicker is that in order to properly test the fan clutch, you have to get the engine hot enough that the air going through the radiator and hitting the front of the fan must be up to 205 F., so the fan clutch will lock. With the fan clutch locked and you making the engine scream at 3,600 RPM, the fan speed should be at least 2,850 RPM.

Now folks, that is one very noisy test. :widegrin:
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Old 01-25-2007, 12:48 AM   #7 (permalink)
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Re: How to tell if fan clutch is bad?

Quote:
Should the fan be able to be stoped if a wooden handle is pressed against it and the truck started briefly?

Yep, it will stop very easily if not engaged. You can do it with a piece of cardboard.

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Old 01-25-2007, 08:03 AM   #8 (permalink)
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Re: How to tell if fan clutch is bad?

Also one more note... When the truck sits overnight/long time without running, that fluid pools at the bottom of the clutch assy. This means when you initially start the truck, you hear the fan running. When all the fluid is evenly distributed via centrifugal force, it will release.

The colder it is, the longer it takes for the "pooled" liquid to distribute. In summer you usually don't even hear the fan cause it disperses the fluid so quickly. I wouldn't even attempt stopping that fan, if something goes sideways at best you may be buying a radiator , worst... ride in rear of paddy wagon.
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Old 01-25-2007, 09:12 AM   #9 (permalink)
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Re: How to tell if fan clutch is bad?

NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NOT EVER, !!NEVER!! STICK ANYTHING INTO A MOVING FAN BLADE!!!!!!!!!

The very *least* that will happen is that you'll damage the fan.

The fan turns all the time the engine is running. The only question is "how fast". Yes, it's supposed to do that. If it didn't, the fan drive wouldn't be able to engage when called for.

CPUNeck did a great job of describing "morning sickness". Yes, that's what it's called by fan drive engineers.

As far as your WVO heater sapping heat at idle, yep, that's normal, too. The engine only puts out so much heat at idle, and if you've increased the heat sink (by adding the WVO heater to the circuit in addition to the standard cabin heater core), the equilibrium point where Q-dot (heat flux) in equals Q-dot out will occur at a lower coolant temperature. You're measuring the temp in your WVO tank, so you see the impact indirectly as a lower WVO temperature.
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Old 01-25-2007, 11:26 AM   #10 (permalink)
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Re: How to tell if fan clutch is bad?

Thanks guys. The fan seems to be operating normally then. I guess with the cold weather and the extended idling there is not enough flow to keep my wvo temps up.
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Old 07-02-2007, 11:12 AM   #11 (permalink)
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Re: How to tell if fan clutch is bad?

Quote:
Also one more note... When the truck sits overnight/long time without running, that fluid pools at the bottom of the clutch assy. This means when you initially start the truck, you hear the fan running. When all the fluid is evenly distributed via centrifugal force, it will release.

The colder it is, the longer it takes for the "pooled" liquid to distribute. In summer you usually don't even hear the fan cause it disperses the fluid so quickly. I wouldn't even attempt stopping that fan, if something goes sideways at best you may be buying a radiator [img]/ubbthreads/images/graemlins/phoney.gif[/img], worst... ride in rear of paddy wagon.
Sorry to bring up an old thread, but this exactly describes how my fan acts on a cool morning. (Say around 75F or so). The truck feels sluggish pulling down my street and out of the neighborhood with the fan ROARING. By the time I'm a mile or so down the road, all is good.

So my question is...is the fluid in the fan replaceable? Does it ever go bad and need to be changed?
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Old 07-02-2007, 12:03 PM   #12 (permalink)
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Re: How to tell if fan clutch is bad?

Fan clutch is sealed.
Clutches do wear out, some fail others just work doggy for a long time.
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Old 07-02-2007, 01:59 PM   #13 (permalink)
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Re: How to tell if fan clutch is bad?

Thanks!
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Old 05-10-2010, 01:05 PM   #14 (permalink)
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Quote:
Yes, it "runs" all the time. The fan clutch is a viscous clutch, filled with a synthetic high-viscosity oil. So even when that viscous clutch is "slipping" it's still drawing a horse or two worth of power from the engine to pull lots of air through the radiators and coolers. When it locks up under full song, it uses about 27 horses from the engine to pull a hurricane through the radiator and coolers.
Question? How do you know it takes 27 horses to run the fan?

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Old 05-10-2010, 02:38 PM   #15 (permalink)
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Originally Posted by William_IV View Post
Question? How do you know it takes 27 horses to run the fan?
Ford design specs, posted here about 10 years ago by an expert such as AutoJim, the cooling guy. (Yes, I was here and active back then). But that's only at full song, such as over 3,300 RPM when dragging a heavy trailer up a steep mountainside in 100 ambient temps. It probably uses only around 15 to 20 horses when it comes on while poking up the pass in direct drive at only 2,300 RPM.

Or it may have been spoken by the International or Ford engineers at either the Indianapolis engine plant or the KTP assembly plant during the 2001 Memorial Day weekend national get-together for about 200 of the members of this website. Yes, I was there too, back when we were Ford-Diesel.com. Or maybe at one of the regional get-togethers I've attended where the Ford and International engineers showed up, including Lake Texoma, Houston, Indianapolis, and Lake George, NY.

Anyway, you can count on it requiring up to 27 horses at full song. Just ask AutoJim.
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