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2006 chevy trailblazer_ls
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Discussion Starter · #1 ·
First of all, let me say that I have searched all the previous threads, so no one needs to say something smart like "Try the search function."

:thx

Now, my questions. The first question that I have is that I read in one thread where the 2005 and older models had a different fan clutch than the 2006 and newer models. My TB is an '06. Are the fan clutch problems still an issue with the new models?

My second question is do I have a "problem" at all? I get a loud roar sometimes when I start my TB, but it only lasts 10-15 seconds and goes away. Is that an issue I need to worry about, or is that normal? In the previous threads that I read some said this was a normal thing and nothing to worry about. Others seemed to think it was NOT normal.

Thanks guys, and I hope you all have a good weekend.
 

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2007 chevy trailblazer_ls
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mmartincpa I have an '07 and mine does the same thing. It seems to do it more now that it is warmer out but never lasts for more than 15-20 seconds or so. I did have the software updated a few months back by the dealership while I was trying to get a startup noise fixed and they looked at the clutch and said it was fine. It turned out to be the alternator. But back on topic there was a few threads I have read that talk about how the fluid "settles". Hope this helps!!!!:thumbsup:
 

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Discussion Starter · #4 ·
No Roadie, I did NOT miss that post

I read every word of it, and in my opinion it does not answer my main question. The roar that I hear...is that normal and "ok?"

Maybe the answer is found in all of the technical talk that I admit I understand very little of, but I still am not sure if I should worry about the roar or not.

Here is part of the Fan Clutch 101 post that hits closest to my question:

This called for another solution. In the latest design of the clutch there is a feature that allows fluid to drain back into the clutch when it's in the off state (parked overnight kind of thing). Now when you start up there is enough fluid to spin the fan up and keep the a/c working before you get out on the road. This feature came online with the launch of the '06 TB.

Ok, so you'd think everything has been resolved - there have been the occasional leaky valves - and here comes the morning fan noise complaints again. This isn't as bad as it sounds - you can do a neutral rev disengagement of the clutch - meaning leave the truck in park and run the engine up to about 2500 rpm (you probably have a rev limiter that stops you there anyhow). The clutch will disengage (you'll hear the noise fade away) and you'll be on your way - or you can go to get a new clutch put in to solve the noise complaint. All clutches are now leak tested during assembly now to make sure this doesn't happen again.
So does the "morning fan noise" caused by the leaky valves = the roar? And is it just a matter of putting up with the noise, or am I risking damaging my TB if I just ignore it? I don't really want to put a new clutch in if it's not necessary. But if I am damaging my TB then I would like to take care of it now before it leads to something worse. Some of the other threads I read seemed to indicate that if I had the roar, I had a problem that needed to be addressed.
 

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2005 chevy trailblazer_ls_ext
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I would say based on my experience that what you are describing is normal. I've rented many TBs from 2005 on, and all of them did it. Most of these rentals had well under 10,000 miles - some under 1000.

Short answer - not to worry! It's when it roars ALL the time, that you need to worry.
I had my fan clutch replaced by the dealer under warranty and it has done that from day 1.
 

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2005 chevy trailblazer_ls
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The #2 upgraded fan clutch came out mid 05, the updated software came with the 05 model year, late 04 production.

I recently had mine replaced with the #3 (most recent) upgrade of the clutch, but not the software. Mine roars about 10-15 seconds, like you say, then goes away. Does it again on restarting it or when it cools down some. Normal, yes. Like others have said, when it roars constantly is when there is a problem. You'll know, trust me!! Of course, my last one did not roar all the time, but dealer said bad while they were replacing the water pump. Lie?? Maybe. Only true way to tell is to hook it up to a Tech 2, command different speeds, and see how it reacts.
 

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GM and Behr had their fair share of problems with this fan clutch, but the noise is not abnormal when starting the engine. Many fan clutches are used to speed up the engine warm-up to save gas and lower emissions by creating more drag on the engine by running the fan at full speed. I believe this is the case with the TB fan clutch as well.

Regular, non-electronically regulated Visco clutches normally have a fail-safe built into them which causes the Visco to run the fan at full speed if the fan clutch fails. The electronic fan clutch should work the same way. Having said that, you need to always keep an eye on the temp gauge.

If the loud roaring noise persists after warm-up I would agree that your fan clutch may have a problem.

Supposedly, one of the main causes for failure is damage to the wiring harness due to the repeated tension on it whenever the engine revs up.
 

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2003 chevy trailblazer_ls
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its normal.
think of it this way.
theres an oil inside the clutch.
overnight- the oil settles at the bottom.
in the morning- when you turn on the engine- that oil is pooled at the bottom.
it causes the fan to spin.
As the fan spins- centrifugal force causes the oil to spread out evenly-- as it does this- youll hear the fan noise slowly diminish- eventually it quiets down.
In cold weather- the oil thickens up some- and may be slower to disperse- so the noise last a bit longer.
 

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its normal.
think of it this way.
theres an oil inside the clutch.
overnight- the oil settles at the bottom.
in the morning- when you turn on the engine- that oil is pooled at the bottom.
it causes the fan to spin.
As the fan spins- centrifugal force causes the oil to spread out evenly-- as it does this- youll hear the fan noise slowly diminish- eventually it quiets down.
In cold weather- the oil thickens up some- and may be slower to disperse- so the noise last a bit longer.
Having the oil run out from between the two discs inside the fan clutch and gathering at the bottom of the clutch should actually make the clutch disengage, as the friction (or stickiness) the oil creates between the two clutch disk decreases when there is no oil between them. The oil should circulate around the clutch very fast after cranking the engine. The viscosity of the oil is what makes the clutch work. While the oil between the discs regulates the slippage between the discs, it does not mean that the presence of oil causes the clutch to disengage. On the contrary, the presence of the oil between the discs and its viscosity are the reason the clutch engages. The presence of the oil provides the necessary grab between the discs to engage the fan.
 
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