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Hi, 2007 4WD FJ Cruiser 150k miles

I am laying out how to replace a fan clutch. It cost me 4g bc it was misdiagnosed in the past by 3 Toyota dealerships and a transmission shop that finally replaced the transmission which made no change. It's very easy.

A few years ago my FJ started making a whooshing sound when starting off. My mpg went from 20 at 80mph to about 10mpg. 3 Toyota dealers hooked up the FJ w no error codes. A former Toyota tech looked at it, replaced the fan clutch for $120 and back to nml mpg and whooshing gone. The tranny shop closed and I couldn't recoup my 4g. This write up is to help you avoid that.

The FJ's fan clutch controls the speed at which the fan spins depending on various driving conditions. Namely speed and temp. If the fan clutch goes bad, no codes are thrown bc it's not monitored. A whooshing sound is ur first clue followed by dropping mpg. If it spins freely then it's complete toast but spinning it otherwise to diagnose the issue is rather tricky. The point is the silicone inside dries up and gets thicker and inhibits fan rotation at higher speeds effectively driving into a wind for the engine.

A new fan clutch cost me $75 from Autozone w a lifetime warranty. The last one lasted me 2 years. It took 30 minutes to do in my work parking lot.
 

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First take the plastic pop rivets off the cover that covers the radiator. There are a few different ways to pop these out but half of mine just broke bc they r 10 years old. I'm replacing them w fresh ones. In some spots, the holes on the cover broke so those areas get new holes and new pop rivets.
 

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Take the antifreeze overflow tank off.

Pop the top off and move aside. Take the bolts out that hold it on and place aside. This will expose the fan cowl.
 

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Take the bolts off the cowl. I was missing a few so find urs. There is a clip attaching a hose on the driver side. Pry that off w a screwdriver and reattach w a zip tie if u break it like I did. Leave the cowl in the engine bay bc u won't be able to get it out easily until u get the fan/fan clutch assembly off. Then u can take the fan out without even taking the cowl out.
 

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The old fan clutch has 4 bolts to take off. Pics of the new fan clutch.
 

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At first I thought I was given the wrong part. As u can see the new fan clutch is smaller and has bolts instead of holes. I used pliers to gently remove the bolts ans measured that the sizing was correct and attached the new fan clutch to the fan and reinstalled it.
 

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Nice write up! But I'm amazed this dropped you 10mpg and that you're now back to 20mpg just from this. Did the clutch going out bind the fan, so it couldn't spin at all? Or was the fran just free-spinning from the air passing over it?
 
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Neither. When the fan clutch silicone gets thick it doesn't just stop working. It doesn't lock up or free wheel. It just starts to sound like more of a whooshing sound especially when getting moving from a stopped position. This is the second time I've done this. I notice the whooshing and my mpg drop.
 

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The only way that the fan/fan clutch could have been absorbing enough energy to create that huge change in fuel consumption would have been for the clutch to been "locked up" and driving the fan at full speed at all times.

With the fan clutch locked up, the fan can absorb several horsepower continuously. At full lockup, an automotive cooling fan can absorb roughly 3.5-7 horsepower, which is a significant percentage of the power required for steady-state cruising at 60 MPH.

Dragging brakes, or any other energy-absorbing component (binding bearing, etc.) would quickly become red-hot if it were to be absorbing several horsepower continuously.
 

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Nice write up! But I'm amazed this dropped you 10mpg and that you're now back to 20mpg just from this. Did the clutch going out bind the fan, so it couldn't spin at all? Or was the fran just free-spinning from the air passing over it?
The fan clutch has only two operating modes:

1. Free-wheeling mode, so that very little torque is transmitted to the fan and it only turns at a tiny fraction of engine speed.
2. Controlled-torque mode, where the fan speed is controlled by the engine speed and the temperature of the air passing over the clutch. The higher the air temperature and/or the higher the engine speed, the more power is transmitted through the clutch and more power is delivered to the fan, resulting in greater airflow through the radiator.

If the fan clutch "binds" or locks up, the fan will turn at full input speed.

More frequently, the seals wear out and some of the silicone coupling fluid leaks out, resulting in diminished torque to the fan, diminished airflow, and eventual engine overheating.
 

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To make sure:

With the engine off - if the fan spins freely the clutch is bad?
 

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It's not that simple, and depends on the temperature of the fan clutch, and how long the engine has been shut off.

Typically, on a COLD start, the fan clutch will transmit enough power to drive the fan at relatively high speed ... hence the very audible "whooshing" sound immediately after a cold start. The clutch disengages after 30 - 120 seconds as the silicone fluid gets re-distributed within the clutch and allows clutch "slip".

Immediately after engine shutdown with a warm engine, the fan should essentially "free-wheel" when spun by hand.
 

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In my experience with this the fan is locked up or has a spot or 2 that you can feel a drag or notchy feeling when rotating the fan.
On a side note, when I worked in the field I had a full size Chevy van come in my shop from a tranny shop and they couldn't figure out the problem and it turned out to be a fan clutch. It had a whooshing sound and the transmission shifted hard.
 

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I had my bumper off to install a trans cooler, and when I got it all back together and fire it up to top off the trans fluid, I hear this wub wub wub coming from the front of the engine. I started to worry it was an internal engine part. Then I saw this thread and the light bulb in my head went off. Of course, 209,000 miles and it makes perfect sense. Just changed it out for a new Aisin fan clutch and the noise is now gone.

There must have been a dead spot in the clutch causing irregular engagement and alternating sounds from the fan.

Thanks again to the FJC forum. It was a cheap fix rockauto $89 shipped and 30 minutes of my time.
 
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The only way that the fan/fan clutch could have been absorbing enough energy to create that huge change in fuel consumption would have been for the clutch to been "locked up" and driving the fan at full speed at all times.

With the fan clutch locked up, the fan can absorb several horsepower continuously. At full lockup, an automotive cooling fan can absorb roughly 3.5-7 horsepower, which is a significant percentage of the power required for steady-state cruising at 60 MPH.


Dragging brakes, or any other energy-absorbing component (binding bearing, etc.) would quickly become red-hot if it were to be absorbing several horsepower continuously.
So we think of the engine producing 230hp but in reality, the actual hp at cruise speed is only 40-70hp. If you have a drag of 3-7hp on the engine from a locked fan clutch, that is a 10%+ loss of efficiency. That can add up in mpg loss.
 
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So we think of the engine producing 230hp but in reality, the actual hp at cruise speed is only 40-70hp. If you have a drag of 3-7hp on the engine from a locked fan clutch, that is a 10%+ loss of efficiency. That can add up in mpg loss.
Actually it takes even less power than that at a 65 MPH cruising speed, even for an FJ with a relatively high drag factor.

Here are the results from one power/fuel consumption calculator for a typical FJ Cruiser, based on an aerodynamic drag factor of .397, a vehicle weight of 4500 lbs, and a frontal area of 31 square feet.

Power required to maintain a 65 MPG cruising speed is about 31 HP, resulting in fuel consumption of just under 20.5 MPG.

My '14 with several hundred pounds of mods and a hardshell RTT slightly beats the fuel consumption rate shown, so maybe my estimate of the frontal area is a little high.
 

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So we think of the engine producing 230hp but in reality, the actual hp at cruise speed is only 40-70hp. If you have a drag of 3-7hp on the engine from a locked fan clutch, that is a 10%+ loss of efficiency. That can add up in mpg loss.
Actually it takes even less power than that to maintain a 65 MPH cruising speed, even for an FJ with a relatively high drag factor.

Here are the results from one power/fuel consumption calculator with parameters representing a typical FJ Cruiser, based on an aerodynamic drag factor of .397, a vehicle weight of 4500 lbs, and a frontal area of 31 square feet.

Power required to maintain a 65 MPG cruising speed is about 31 HP, resulting in fuel consumption of just under 20.5 MPG. Note that ~24 HP is required to overcome aerodynamic drag, while only 6 HP is required to overcome rolling resistance.

My '14 with several hundred pounds of mods and a hardshell RTT slightly beats the fuel consumption rate shown, so maybe my estimate of the frontal area is a little high.
 
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