2002 Trailblazer cooling fan on high all the time

[mrdctaylor]

Guys,

My daughter has a 2002 Trailblazer with with i6. Recently we had her air conditioner fixed and while we were at it the mechanic told us her cooling fan clutch was in bad shape (lots of play). We had noticed vibration etc. so let him replace that too.

Now the fan seems to be on high from the moment you turn on the car. When you accelerate ithr fan sounds super loud. I took it back to him once and he thought he may have gotten a bad fan clutch so replaced it agin. It is doing the same thing.

Any ideas? Could it be something else? Thoughts? I’m going to have to take it back again but I’m trying to gain a little more knowledge before I do.

Thanks!

 

[Alex_V]

The fan that's "on high all the time" - do you mean the mechanical fan or the electric assist fan? I'm not sure if that has both or just the belt driven one.

A lot of replacement fan clutches don't behave quite the same as the original. The one from Napa I put in my '85 GMC hooks up hard until about 50 MPH then slacks off - the truck gains about 3 MPH when it does, just from the reduced drag. But when I'm pulling something, the coolant temp starts to rise, and that sucker hooks up, you hear and feel it roaring even over highway noise and a 60 MPH wind through the open windows.

 

[mrdctaylor]

Honestly, I'm not sure. I just hear the fan running full bore when she takes off with a cold engine and I know the original did not do that. I don't drive her vehicle enough to know if it begins to act right once it has been driven for a while. Maybe it *is* working, but just not like the original. I was under the impression that the fan generally wasn't supposed to come on when the engine is cold. Maybe I'm all mixed up on that. I just know that when she used to start her car, it was super quiet. Now it has the fan going full blast.

 

[dlundblad]

The mechanical fan will run full bore when cold because it's been sitting and all the fluid is in the center of the clutch. Once the engine spins, the fluid should move outward and cause the clutch to function. Once it's hot, the thermal band will move cause the valve to close and engage the fan. Likewise, as you are cruising down the highway, the thermal band should move and open the valve and disengage the fan. (No loud fan noises or dragging engine.)

When the engine is hot and has been running a while, pop the hood and stick a roll of newspaper in the fan and see if it stops the fan. If it just shreds the paper and continues to spin, I say you have a defective clutch.

YouTube how to use newspaper to test it. I don't want to be responsible for you losing your finger(s). Lol

 

[mrdctaylor]

Thanks--that's great information. I like all of my fingers as they are, so I'll act accordingly. ;-)

 

[maxdustington]

Originally Posted By: dlundblad
The mechanical fan will run full bore when cold because it's been sitting and all the fluid is in the center of the clutch. Once the engine spins, the fluid should move outward and cause the clutch to function. Once it's hot, the thermal band will move cause the valve to close and engage the fan. Likewise, as you are cruising down the highway, the thermal band should move and open the valve and disengage the fan. (No loud fan noises or dragging engine.)

When the engine is hot and has been running a while, pop the hood and stick a roll of newspaper in the fan and see if it stops the fan. If it just shreds the paper and continues to spin, I say you have a defective clutch.

YouTube how to use newspaper to test it. I don't want to be responsible for you losing your finger(s). Lol


The inner child in me wants to find a car with a mechanical fan and try this.

 

[dlundblad]

Originally Posted By: maxdustington
Originally Posted By: dlundblad
The mechanical fan will run full bore when cold because it's been sitting and all the fluid is in the center of the clutch. Once the engine spins, the fluid should move outward and cause the clutch to function. Once it's hot, the thermal band will move cause the valve to close and engage the fan. Likewise, as you are cruising down the highway, the thermal band should move and open the valve and disengage the fan. (No loud fan noises or dragging engine.)

When the engine is hot and has been running a while, pop the hood and stick a roll of newspaper in the fan and see if it stops the fan. If it just shreds the paper and continues to spin, I say you have a defective clutch.

YouTube how to use newspaper to test it. I don't want to be responsible for you losing your finger(s). Lol


The inner child in me wants to find a car with a mechanical fan and try this.


I stuck my hand in mine on accident while checking something else under the hood. Thankfully it was disengaged and just smacked my fingers really hard as opposed to removing them.

 

[maxdustington]

Originally Posted By: dlundblad
I stuck my hand in mine on accident while checking something else under the hood. Thankfully it was disengaged and just smacked my fingers really hard as opposed to removing them.


I am glad that modern cars have electric fans, the fans on my car are against the radiator.
I like old cars more though, the ones that tend to have giant metal bladed cooling fans.

 

[oldmaninsc]

If I remember correctly, these vehicles have an electric fan clutch. Checking Rock Auto seems to verfiy that.
https://www.rockauto.com/en/moreinfo.php?pk=1028594&cc=1398719&jsn=453

The problem most of us had with the factory fan clutch was it didn't run fast enough at low speed for the A/C to cool properly. I seem to recall GM had about 3 or 4 updates to the original fan.

When I was a member of the Trailblazer forum we always recommended an OEM clutch because the aftermarket were copies of the original bad design.

 

[mrdctaylor]

Well, this one DEFINITELY seems to run fast enough at low speeds! Maybe I was used to hearing one that did not. It just seems to be running too fast at idle. I probably need to drive my daughter's car for a bit and see if I can understand what's going on more. If the fan clutch disengages after a few minutes, it may be OK. It just sounds so loud when she takes off from my house after she comes for a visit.

 

[oldmaninsc]

I sold my Trailblazer back in 2010 or 2011. I do remember the new fan clutch on mine being loud at start up. IIRC it wasn't as loud a few minutes later. I bought mine new Jan. 2005 so it's been a while and as they say - the memory is the first thing that goes.

The mechanical fan clutch in my Ford Aerostar is loud for about a minute after start up. Always was, even after I replaced the fan clutch with a new OEM.

 

[Nick1994]

The first couple years of the Trailblazer had a defective fan clutch, plenty to read about them on the TrailVoy forums. There's an updated part number. My grandparents had a 2002 that I maintained, we had the fan clutch replaced because it was running warm and the a/c sucked. New fan clutch and it was fantastic afterwards. It would then roar a little on startup and while driving for the first block or two. If it sounds like a jet engine, it's probably bad.

 

[mrdctaylor]

Originally Posted By: Nick1994
The first couple years of the Trailblazer had a defective fan clutch, plenty to read about them on the TrailVoy forums. There's an updated part number. My grandparents had a 2002 that I maintained, we had the fan clutch replaced because it was running warm and the a/c sucked. New fan clutch and it was fantastic afterwards. It would then roar a little on startup and while driving for the first block or two. If it sounds like a jet engine, it's probably bad.


Well, it may be more of a roar than a jet engine. I guess it is subjective. I need to do a little more troubleshooting to see how it acts after the first few minutes of driving.

 

[Nick1994]

The one on my grandparents simply stopped working, usually what happens on the Trailblazer fan clutches is they lock up, and that's what people describe it as, a jet engine. Super loud.

 

[gonefishin]

I've replaced the fan clutch in my 2004 Trailblazer. It has been years ago but I recall mine doing the same thing after the install. After sometime it did settle down. It is my understanding the PCM has to re-learn the new clutch. Much like if you disconnect your battery with a dirty throttle body, the truck will run rough as the PCM thinks you have a clean throttle body which it does not. It's a re-learning process. If however this continues for some time, take it back to your mechanic and explain the issue.

 

[Falcon_LS]

Although the engine spins the fan, the fan clutch on the GMT360 platform is controlled by a PWM signal - it's an Electro-Viscous (EV) fan. At 600 rpm with the AC off, the fan spins at ~750 rpm, moving about 2,050 CFM of air. When the AC compressor runs, the PCM commands a 10% higher fan RPM. When you're driving 60 MPH on a flat road, the commanded RPM is in the 800 rpm range.

I don't know what your replacement clutch is, but I would not recommend aftermarket fan clutches for this application. Initially, for noise reduction purposes rubber buttons were built into the opening valve, which is controlled by the EV unit (coil). Shims controlled the valve lever, and the clutch's fluorosilicone buttons literally fell off as the unit aged with exposure to silicone fluid. GM engineers later redesigned the clutch with a mechanical stop instead of an EV unit. For fuel economy reasons, the PCM was programmed to operate at 80 PWM (initially 100 PWM). This then brought about another issue, which caused the clutch to tick like crazy and the clutch was redesigned again to allow fluid to drain back into it when the engine was not running. This was in mid year in 2005 for MY2006, and vehicles produced after 06/2005 got the updated part. The OEM for the clutch is Hella-Behr (P/N 376734021), which you can buy on RockAuto for $138. The OE part in an ACDelco box (P/N 15-40133), which is the same part, costs $219 in comparison.

The reason I would not recommend aftermarket units (other than the OE Behr unit obviously) is because many still utilize the old design with rubber buttons in the valves. My suggestion - replace the clutch with the OE part and reset the PCM.