fan clutch diagnosis

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I drove my wife's Sequoia yesterday and am wondering about the "roar" coming from the engine bay. The 4.7 liter always makes this roaring noise on initial cold start-up which I am assuming is normal. It lasts maybe 15 or 20 seconds and goes away.

However, yesterday we were running a little late for our baseball game so I was a little heavy on the throttle. Anytime the engine downshifted or rpm's increased I got the same roar coming from the engine. Sounds like a jet taking off! I don't drive it much but I don't recall this happening before.

Is this the sign of a failing fan clutch? What is the best way to diagnose? I have heard they can be rebuilt or new fluid put in them if bad? Doesn't seem to be overheating but we don't do much stop and go traffic out here in the country. Any suggestions? thanks.
 
Mechanical fan clutches (as on my BMW) always make noise on startup, that is normal. But on cooler days it should stop in less than a minute. If it continues to make noise then it is either hot out or the clutch is seized.

No they can't be refilled (well at least not the ones I've seen). One way you can test it is to hold the fan steady with a rolled-up newspaper as you start the car. You should be able to keep the fan from turning with the newspaper as the engine starts. You don't jam the paper in like a stick on your bicycle wheel, just use it to hold the blade steady.

The clutch can be relatively expensive, one reason is that they are often filled with a perfluorocarbon or fluorosilicone fluid which is pricey.

Originally Posted By: wolfehunter
I drove my wife's Sequoia yesterday and am wondering about the "roar" coming from the engine bay. The 4.7 liter always makes this roaring noise on initial cold start-up which I am assuming is normal. It lasts maybe 15 or 20 seconds and goes away.

However, yesterday we were running a little late for our baseball game so I was a little heavy on the throttle. Anytime the engine downshifted or rpm's increased I got the same roar coming from the engine. Sounds like a jet taking off! I don't drive it much but I don't recall this happening before.

Is this the sign of a failing fan clutch? What is the best way to diagnose? I have heard they can be rebuilt or new fluid put in them if bad? Doesn't seem to be overheating but we don't do much stop and go traffic out here in the country. Any suggestions? thanks.
 
Fan "roar" is normal for 10-20 seconds on cold start. The fan is locked until the fluid shears out of the way and allows the clutch to freewheel.

Start it up, run for a minute until the roar goes away. Stop engine and spin the fan. It should be fairly "loose". Likewise, after it is warm, like in city driving idling with AC on, give the fan a spin to verify it has some resistance. I am unsure of your setup and whether it has any additional electric fans. Clutch setups on engine driven fans, with additional aux electric cooling fans is a bit different. The main fan doesn't kick in/apply clutch until the engine gets really warm....sometimes. A lot of times they are hard to diagnose as common sense says it should be locked, but it is still loose and freewheeling on a warm engine. All for addl. mileage.

Some fan clutches can be rebuilt (like on large commercial trucks) but it is rare to have a rebuildable one on a light vehicle. I guess if the clutch is an aluminum casting, bolted together, it might be rebuildable. Many clutches now are made of parts with one side aluminum, and the front stamped steel and crimped for a seal.
 
Fan clutches usually Lose efficiency as they age. They lose fluid and the vanes inside get worn down. You may have an overly aggressive one or one that's frozen and turning all the time.
 
Originally Posted By: punisher
A lot of times they are hard to diagnose as common sense says it should be locked, but it is still loose and freewheeling on a warm engine.


The way I actually diagnosed it on my BMW (which does also have an electric fan) was that I could hear my daughter coming down the road a quarter mile away. Like you imply you could spin it by hand when stopped, but it still was "broken". Once replaced the full time roar stopped.
 
The newspaper test is what I always learned/knew to be the right assessment, assuming it is a mechanical clutched fan and not electric drive.
 
With the engine off, cold, spin the fan by hand. Should spin easily. Start the engine with the hood up, cold, then shut it off, it should freewheel for a 2-3 seconds. Do this again with a hot engine, it should still turn by hand & freewheel, but with more resistance. if it's very hard to turn, then the clutch has failed.
 
I changed the fan clutch on my old trusty 4runner last year. Best price for an OEM Aisin unit was from Amazon. Around $60, if memory serves. The original lasted 245k miles, so I didn't got for a cheaper alternative.

I recovered a full 1mpg. The new clutch should pay for itself, sometime in the next decade.
 
Originally Posted By: CT8
The biggest fail in when the car overheats.


Or.....When the clutch comes apart, and the fan enters the radiator.

Most of them seem to drive the fan continuously, when they fail.
 
Car is 10 years old with pretty low mileage(60K). Is it odd for one to fail so soon?

Also wondering why it seems to function normally on cold start running for 15 to 20 seconds and then stops. But once the vehicle is warm and I increase rpm's I hear it again. Does that mean the clutch may not be working which makes the fan spin as fast as the water pump is spinning in accordance with rpm's? Which translates to frozen or seized?
 
Could it be that you were heating the engine up enough that it started to engage more? When I had one that was designed for my Cherokee, driving it slightly harder, even, would cause it to engage more to keep the engine cool.

I swapped on a fan clutch from a 4 cylinder cherokee and now mine roars all the time. That's okay with me.

As for how long they last - that is all dependent on the vehicle itself.
 
Originally Posted By: wolfehunter
Car is 10 years old with pretty low mileage(60K). Is it odd for one to fail so soon?

Also wondering why it seems to function normally on cold start running for 15 to 20 seconds and then stops. But once the vehicle is warm and I increase rpm's I hear it again. Does that mean the clutch may not be working which makes the fan spin as fast as the water pump is spinning in accordance with rpm's? Which translates to frozen or seized?


Perfectly normal behavior for a fluid clutch design. After a few seconds they disengage normally. Since many are thermostatically operated they will roar again as things get hot.

Note that in our fleet trucks used in stationary operations a fluid clutched fan is generally good for 2-3 years. Typically we notice decreased AC performance as they wear out...
 
I had a fan clutch fail in a V8 tundra at around 150k miles, probably the same clutch. The biggest difference I noticed was that with the failed one, the roar kept getting louder as the rpm increased above 3k. The OE replacement seemed to limit Dan speed to around 3k even as the engine accelerated towards redline. With the working OE clutch, it would stay locked at low RPM pretty much all summer if the A/C was on.

In my case the bad clutch would do the normal roar when cold, then get quiet, then stay locked once warm.

My current vehicle has a bad fan clutch that is doing something similar, and I just noticed that the fan has multiple cracks around the hub. New OEM clutch and fan will be here tomorrow. Hopefully I can make it through the day without it coming apart.
 
On my BMW when it failed it never engaged to spin up to higher speed. It would constantly turn at low speed (no roar).

My brand new clutch gives me that roar on startup. I also get it when I turn on my AC. That's one way you know your fan clutch is working properly.

AC works great after replacement as well.
 
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Sometimes they can be refilled. The AISIN one on my 4Runner can be taken apart, the fluid dumped, and new fluid put in. It's just silicone oil of 3000 cst or 5000 cst viscosity (higher viscosity gives tighter coupling). You can find this fluid at a hobby shop for RC car shocks.
 
The fan clutches in the Sequoias and Tundras can be refilled. There is a Toyota part number floating around some of the various forums for the correct viscosity oil that supposedly is available at most Toyota dealers. There was a thread on the Tundrasolutions forum about this not too long ago.
 
Update: AS I was checking the resistance of the fan speed cold the other morning before leaving for work I found the problem. All four latches of the air cleaner housing lid were open! I have no idea how this happened but the "roar" was obviously coming as the intake was sucking air out of the engine compartment. Glad it was an easy fix! Thanks for the assistance.
 
Always check your engine Temps manually before assuming anything about the clutch.

One time when my Navigator was overheating, I heard it roaring like crazy. It was reacting to the extreme engine Temps that my dummy analog-style gauge does not display.
 
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