Fan clutch engagment?

---2005---D/A 3500/CC DRW---
I was woundering if others would share their experiences with their cooling fan clutch engagement characteristics. My experiences are as follows. When I first recieved the truck I had an intermittent chirping noise(close to the sound of brake pad wear indicter on a warped roter) from the engine area at lite throttle and low speeds(20-35mph). It did not match vehicle speeds but closely followed engine speeds. I visited the dealer and after a test dive was told "This is normal diesel eng noise" and when I ask him if he pacifically herd that noise in other diesel engines, his responce was "Well no,I do not normally listen to them that closly ". Time to find another dealer. Two days later, with about 600 miles on the truck, the noise became really consitent and and a bit louder untill leaving a stop lite it disaperred for good. The following mourning on first startup the fan clutch was engaged (first time I have even heard the fan)and stayed engaged for about 5 miles. Now the fan clutch intermittenly is engaged on first startups and after short distance disengages never to engage again during the drive. Two weeks ago I left on vacation with 5th wheel(11,000pounds) in tow to nourthern lower Mich.(now 1200 miles on truck). Lite hilly terrain with temps at mid 60's night and around lower 90's day running at 70mph. Regardless if I am pulling a hill or running flat land, in early mourning or mid after noon, a/c on or off fan cluth seems to engage for no rime or reason. Now when this clutch engages at 70mph(about 2200rpm) you sure know it and on some hills will couse the trans to down shift(now engines at about 2900rpm). Now from what I understand about cooling fan is that at about 30-35mph the incoming air through the grill will overcome anthing the fan can pull. While all this is happing the trans and eng temps are rock solid at 190/200 deg. Upon returning from vacation I took the truck to a differant dealer and was called today and told that GM considers all this to be normal. I find this hard to believe and would like to here what others are experiencing.

Welcome to the forums!

Excellent details. Other than your noise, it sounds very typical and normal to me. The fan clutch responds to the actual temp of the air passing through the radiator, and nothing else. When it is cold, the fan clutch should engage/disengage until the fluid inside warms up and flows more freely. This can be several minutes, as you have seen. After the engine is up to operating temp, the opening/closing of the thermostat will determine the clutch operation. The A/C condensor will add some heat, but by itself is not enough to effect the fan clutch. The Duramax fan clutch is much more aggressive than any OEM's I've seen on other vehicles. The fan is very efficient, and relatively quiet. It will pull more air through the radiator than is possible with just ram air.

The noise?? Could have been a factory new item wearing in. My guess would be a pully, or just a squeeky belt. Either is not common, but will be considered normal as long as it goes away and nothing else is discovered wrong.

In addition to what DmaxMaverick mentioned:

Due to the fluid settling characteristics, these fan-clutches usually engage after the engine has been shut-off for a time - whether overnight or several hours. The fan-clutch will disengage after a half mile or so of driving. This is normal.

A thermostatic coil on the front of the fan-clutch controls engagement while the engine is running, and will react to changes in heat felt by the coil. The Allison ATF cooler, A/C condenser, intercooler and radiator all add heat to the airflow entering the engine compartment through the grille. Once the temperature reaches a predetermined level, the thermostatic coil on the fan-clutch will engage the fan.

Incidentally, it appears the fan-clutch engagement calibration used with the LLY is somewhat higher (higher cut-in temp) than those used with the LB7. This, in part, explains why more LLY owners report wider fluctuations in engine temperatures (does't engage as often as an LB7). I suspect GM became weary of dealing with warranty owner concerns about fan noise (possibly misinterpreted as something more serious), and so raised the fan-clutch engagement temperature.

As to the noise you're hearing. It could be a belt tensioner, A/C compressor, or belt slip.

MP

Still sifting through the details, but it does seem that the clutch comes in higher (later) on the LLY even though the part number is the same.

Well after talking to the tech. he will be installing a new fan clutch tomorrow. I will be letting him and you know if there is any change in condition. Although I know that what I discribed sound and for the most part is normal fan clutch operation, I do beleave that what I am experiencing is a little to agressive fan clutch. After running with the new fan clutch I will post my results. Thanks for the replies.

My experience with these clutches is that they tend to be very accurate within a 10

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Originally posted by MONTYX5:
---2005---D/A 3500/CC DRW---
I was woundering if others would share their experiences with their cooling fan clutch engagement characteristics. My experiences are as follows. When I first recieved the truck I had an intermittent chirping noise(close to the sound of brake pad wear indicter on a warped roter) from the engine area at lite throttle and low speeds(20-35mph). It did not match vehicle speeds but closely followed engine speeds. I visited the dealer and after a test dive was told "This is normal diesel eng noise" and when I ask him if he pacifically herd that noise in other diesel engines, his responce was "Well no,I do not normally listen to them that closly ". Time to find another dealer. Two days later, with about 600 miles on the truck, the noise became really consitent and and a bit louder untill leaving a stop lite it disaperred for good. The following mourning on first startup the fan clutch was engaged (first time I have even heard the fan)and stayed engaged for about 5 miles. Now the fan clutch intermittenly is engaged on first startups and after short distance disengages never to engage again during the drive. Two weeks ago I left on vacation with 5th wheel(11,000pounds) in tow to nourthern lower Mich.(now 1200 miles on truck). Lite hilly terrain with temps at mid 60's night and around lower 90's day running at 70mph. Regardless if I am pulling a hill or running flat land, in early mourning or mid after noon, a/c on or off fan cluth seems to engage for no rime or reason. Now when this clutch engages at 70mph(about 2200rpm) you sure know it and on some hills will couse the trans to down shift(now engines at about 2900rpm). Now from what I understand about cooling fan is that at about 30-35mph the incoming air through the grill will overcome anthing the fan can pull. While all this is happing the trans and eng temps are rock solid at 190/200 deg. Upon returning from vacation I took the truck to a differant dealer and was called today and told that GM considers all this to be normal. I find this hard to believe and would like to here what others are experiencing.

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GO TO THE 6600 MAIN SITE AND READ THE POSTINGS ON FAN CLUTCH, I ALSO HAVE THE SAME STUFF GOING ON!

Is there an electric fan for the Duramax to replace the clutch fan?

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Originally posted by REDTRUCK05:
Is there an electric fan for the Duramax to replace the clutch fan?

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No

You'd be hard pressed to get an electric that would move the same volume of air. If you did, you'd probably need a bigger alternator and a dedicated battery.

Redtruck05 where is the 6600 main page you are speaking of dude I wanna read more on this topic. Thanks

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Originally posted by turner fuel up:
Redtruck05 where is the 6600 main page you are speaking of dude I wanna read more on this topic. Thanks

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Welcome to the forums!

If you found you way here, you're in it.

The Duramax 6600 page.