It seems that the fan clutch on my truck is always engaged. When sitting there idling you can here the fans keep speeding up then slow down for a couple seconds and then speed back up. Then with the recent cold spell here in Northern Ohio I turned on the High Idle. Now when the high idle kicks in the fan sits there and screams away the entire time. So I had an appointment for the truck to go to dealer already and told them about the what I thought was the problem. They tell me that it is acting normal and that it is from the winter cover that I put over the grill cuz the engine is overheating. So I explaned to them that This was when the engine is cold not when it is warm, and I only put the cover on because in my short commutes around town I couldnt get the engine to break 150*f. So I don't think they are going to do anything. This is my first diesel/duramax, but not the way I remember the mechanical fan on my last gasser acting. Is this normal? I have to pick the truck up tomarrow morning from dealer and would like to know if this truelly in normal operation, or if it is a bad clutch.

Thats the same as my 05 is doing, even when I start it from cold in the morning, the fan is cycling on and off,

Doesn't sound right. Mine only comes on when towing and higher loads/temperatures.

It doesn't sound anything like mine. If you take off the cover, and it still happens, then you proved the dealership wrong.

I've had 5 vehicles with the auto clutch fans. Each one, occassionally, has the fan engaged when starting cold. It disengages within about 30 or 40 seconds of driving. Never reengages itself unless I'm in heavy traffic on a hot day. You can definately feel and hear it cycle. Since all five different vehicles demonstrated same type of fan performance I don't think anything is out of line.

Mine does the same thing. You can start the engine when it is 20 below and the fan is cycling on & off. If there is a reason for it I sure would like to know. Seems kind of ridiculous when you are running it to warm it up. When I asked the dealer they did'nt have any idea's. We went out and check all the other new 05's on the lot & they did the same thing. The dealer could not get any answers from GM so I tried with GM calling customer service and never did get an answer.

ACC, do a search, this is normal for most any viscous clutch.

There have been many threads here regarding cold/first start engagement.

Mine does the same thing. You can start the engine when it is 20 below and the fan is cycling on & off. If there is a reason for it I sure would like to know. Seems kind of ridiculous when you are running it to warm it up. When I asked the dealer they did'nt have any idea's. We went out and check all the other new 05's on the lot & they did the same thing. The dealer could not get any answers from GM so I tried with GM calling customer service and never did get an answer.20 below?that's just too cold!:eek:

I realize how a viscous clutch works on start up. On a gasser it will run for 30 to 40 seconds and then won't run till the engine gets hot enough. Why on the D/M does it continue to run when the engine is cold and your using the high idle feature to try warm it up. Kind of defeats the purpose. It is an electronic system. The only thing I can figure out is it is running because of the after cooler. But I am just guessing.

I realize how a viscous clutch works on start up. On a gasser it will run for 30 to 40 seconds and then won't run till the engine gets hot enough. Why on the D/M does it continue to run when the engine is cold and your using the high idle feature to try warm it up. Kind of defeats the purpose.

That is what I thought, that is why I mentioned it to the dealer. When my high idle kicked in the fan was running so fast, truck outside in drive you could hear it in house 60+ft away. Back in 50's here now, will wait till gets cold again to see how it acts.

My truck also engages on cold start up. But after 30 seconds of driving it shuts off. But if I let it sit and idle it will continue to engage and disengage for a while. At first i thought something was wrong, but after a short drive it shut off and will not re-engage until the motor is hot, like while towing.
Jason

That is what I thought, that is why I mentioned it to the dealer. When my high idle kicked in the fan was running so fast, truck outside in drive you could hear it in house 60+ft away. Back in 50's here now, will wait till gets cold again to see how it acts.

You might try parking it at the dealership overnight, then go over first thing in the morning and start it with a tech standing by. What you describe doesn't sound normal, it should free spin after a few minutes. Good luck. JJ :)

I did that. They had no explanation.

I did that. They had no explanation.

If you have the option of trying another dealer you might try that. Otherwise go knock on the service managers door and make your case. If that doesn't cut it the General Managers office would be next. Then ..... The old saying the squeaky wheel gets the oil runs true, SQUEAK! ):h JJ :)

As I had said in one of my previous posts. I have already tried with GM and got no where.

My truck also engages on cold start up. But after 30 seconds of driving it shuts off. But if I let it sit and idle it will continue to engage and disengage for a while. At first i thought something was wrong, but after a short drive it shut off and will not re-engage until the motor is hot, like while towing.
Jason

Mine does the same.

As I had said in one of my previous posts. I have already tried with GM and got no where.

Sorry about that! GM meaning the General Manager of the dealership.

Just for kicks take him/her out and start one of their new Duramax trucks when it is dead cold and see if it does the same thing. If not that should convince them.

If the fan stays engaged in very cold temps the truck is going to run too cold which adversely affects performance and MPG's. Do a search on "thermal viscous clutch" in this forum, I know someone posted good intel on just how they work. Normal for them to engage first thing in the morning, it is supposed to release and only engage when sufficient BTU's are present.

With constant engagement, especially in cold temps, you are overcooling the coolant, engine, etc. All they need to do is change out the fan clutch, simple evolution. Has to be very frustrating. Good luck! JJ :)

acctech

I'll take a stab at this. You have a thermo-viscous clutch with no intelligence circuitry. It will/can come on in the morning when cold, due to design (not the greatest feature of which is the use of neutonian silicone viscous slip fluid which can be very thick in the cold morning). It will be somewhat trapped in the "engagement channels" until it is worked out through centripetal force. The motor has to be spun up around 2000 rpm for some time to get this to happen. Once you hear the fan kick out, it should stay out.

What you may be hearing at low idle, and I have made this mistake, is the egr valve cycling. To me it give the motor a distinctive pitch change that resembles fan clutch cycling.

Truth is, in the morning, at low idle, the clutch is engaged (usually, varies from truck to truck and how hot it was before shutdown).

You just can't hear it at 800 RPM, it doesn't make a lot of noise till around 1200+.

Hope it helps.

KillerBee thanks for the expanation. I was really hoping there was something wrong because I just think that the high idle would be more effective if the fan wasn't engaged.

Also my tempature gauges start out at 170-175 in the morning just up on the gauge some, is this normal, or do you think I have a bad gauge or temp sensor. Thanks for everyones help.

KillerBee thanks for the expanation. I was really hoping there was something wrong because I just think that the high idle would be more effective if the fan wasn't engaged.

Also my tempature gauges start out at 170-175 in the morning just up on the gauge some, is this normal, or do you think I have a bad gauge or temp sensor. Thanks for everyones help.

The gauge is off I think. Normally start out off the scale,

It sounds like you have a bad sensor somewhere. My guages start off the scale and as temps rise, so do they.