'08 9-7x 4.2i. Sometimes when I start the truck the fan is on, for what seems to be for no reason at all. Sometimes it's hot out, sometimes it cold out. It will be on from startup and usually only stays on about one minute. Any ideas?
Reason for fan at startup?
- Thread starter MindBlowin03
- Start date
Which fan? The HVAC cabin blower or the engine cooling fan?
Assuming it's the HVAC cabin blower, it could be a failing speed control module. Do you have the automatic (digital control) system?
Assuming it's the HVAC cabin blower, it could be a failing speed control module. Do you have the automatic (digital control) system?
shrek77
Member
- Mar 30, 2012
- 252
I am assuming the clutch fan is what he is talking about. The clutch fan in our TB 4.2 is an electronically controlled visco clutch. which means there is silicone fluid that is transferred between an internal reservoir to a working area and is controlled by the opening of a valve. Sometimes the valves can leak causing the fan to engage when starting on occasion. The leaky valve is a positional problem, meaning sometimes it will give you a noisy clutch and sometimes it won't. It depends on what position the clutch stops in after shut off. This won't hurt anything and if it does not disengage and always stays engaged then it likely would need replaced.
BlazingTrails
Member
- Apr 27, 2014
- 19,409
Doesn't an 08' have the newer thermal fan clutch? If so they all do that for a moment until they break loose. If you rev it up to 1500 rpm for about 5 seconds you should notice the fan noise stop. If this is the case it is completely normal.
Mooseman
Moderator
Yep, the '08+ use the newer (actually older) thermal clutch fans that have been around since the 70's. Depending on the particular design, it might pull more air until the silicone in the clutch loosens up a bit and lets the fan freewheel. It would probably do this more if the engine is cold. Also possible that if the engine is hot when it's shut down and restarted a little later, the clutch may have "thermal soaked" the heat from the engine and engaged the fan and once running again, cooled down and disengaged.
Mine does this... usually by the time I pull out of the driveway it quiets down.... My old blazer did the same thing.Mooseman said:
BlazingTrails
Member
- Apr 27, 2014
- 19,409
Just checked back in. From what Ive been told the '08 does have the newer(but older) style fan clutch. Next time it does this I am going to free rev like BlazingTrails suggested. I will post back with the results.
Ok, update. Haven't driven the truck in about a day. Just started it up, about 70* and cool out, and the fan was on. I immediately revved it to 1800 RPMs or so for aobut 10 seconds and nothing. Drove it down my block in 1st so I kept the RPMs at about 2000. This lasted about 10-15 seconds and nothing. Stopped at the stop sign for about 10 seconds(traffic), pulled out and it was gone. I say it lasted a total of about 45-60 seconds.
BlazingTrails
Member
- Apr 27, 2014
- 19,409
That is a little longer than usual, but it's not really going to cause a problem. If it is bothering you go ahead and replace it. But please only use ac Delco, aftermarket brands will sometimes be worse than yours. I really think it will be fine tho
Ok thanks. I will leave it alone unless it gets really bad. I just didnt know if this was an issue or not.
Mooseman
Moderator
Yeah, I wouldn't bother with it neither. Check to see if there is any leakage at the front of the clutch at the thermal spring (you would have to unbolt and move the fan shroud) and check to see if there is any radial movement (rock the fan back and forth as if you were checking the bearings on a wheel). If you have either of these, it's due for replacement but not urgent.
Paul Bell
Member
- Aug 16, 2014
- 460
As I recall from my years of having cars with the old school thermal fan clutch, when it's on cold start-up, it takes a short while for the viscous fluid to let go or catch up to what it's supposed to be doing.
On the older GMT360/370 trucks with the PCM controlled fan clutch, as with many things the PCM controls & monitors, it probably does a start-up test and looks for the proper feedback from the speed sensor in the clutch. The PCM performs a few tests on start-up.
On the older GMT360/370 trucks with the PCM controlled fan clutch, as with many things the PCM controls & monitors, it probably does a start-up test and looks for the proper feedback from the speed sensor in the clutch. The PCM performs a few tests on start-up.
RayGumm
Member
- Apr 16, 2014
- 630
I have an 06 with the PCM controlled fan and the Engine cooling fan will be on at startup every single time. takes about 30ish seconds to quiet down. It seems to have done this since we bought it back in April.
Does it when its hot OR cold outside, and when the engine is hot OR cold or just warm. Nothing seems to make a difference, it just comes on. I probably need a new fan clutch but realistically I am not too worried about it until the thing either quits altogether or stays full bore on all the time. Then I will deal with it.. Might even do an E-fan setup to gain some room by deleting that damn fan shroud...
Does it when its hot OR cold outside, and when the engine is hot OR cold or just warm. Nothing seems to make a difference, it just comes on. I probably need a new fan clutch but realistically I am not too worried about it until the thing either quits altogether or stays full bore on all the time. Then I will deal with it.. Might even do an E-fan setup to gain some room by deleting that damn fan shroud...
Paul Bell
Member
- Aug 16, 2014
- 460
Fan roar on startup may be normal as the PCM goes through it's startup and functions tests. After it runs the test, the fan clutch releases and it slows down.
I've recently installed a new Hayden 3200 fan clutch and it does exactly this. Locked on startup resulting in fan roar, slows down and quiets down within a minute.
I doubt you need a new clutch. Change to a new one and it may do the exact same thing-as it appears it's supposed to.
Fan operation seems to be a bit of a mystery-for startup and operation at highway speed. Nobody here knows for sure. I'll be doing a monitoring test with a tech tool in the next week or so.
I've recently installed a new Hayden 3200 fan clutch and it does exactly this. Locked on startup resulting in fan roar, slows down and quiets down within a minute.
I doubt you need a new clutch. Change to a new one and it may do the exact same thing-as it appears it's supposed to.
Fan operation seems to be a bit of a mystery-for startup and operation at highway speed. Nobody here knows for sure. I'll be doing a monitoring test with a tech tool in the next week or so.
I just wanted to check back in with a small 'update'. I still get the random fan clutch 'issue' but recently I have been hearing a small clicking sound coming from the fan area as well. Is that another hint that the clutch is going out? Im thinking I should just go ahead and replace the fan clutch with a new ACDelco unit.
Mooseman
Moderator
It could be on its way out but you should check to be sure it's not something else like a belt idler bearing or the water pump. Hayden is the preferred brand here. RockAuto has them for $80 + 5% off with codes available here. If you prefer ACDelco, they have them too at $99.
Paul Bell
Member
- Aug 16, 2014
- 460
AHH thank you.MindBlowin03 said:
Rock Auto lists the PCM electrically controlled version AND the thermal only unit for the 2008 trucks.
Perhaps both were available. Whichever one you need, the Hayden version will do you well and save you some cash over the ACDelco version.
Mooseman
Moderator
