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Duramax Fourth Generation: 2007.5-2010 (LMM) Discuss the fourth generation (2007.5-2010) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 06-20-2019, 02:45 PM   #1 (permalink)
Jimpa
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Temp increase at idle

Instead of my engine cooling down at idle, the temp will increase. I've watched it go from 190 while driving in 105 degree weather to 220 while at idle after approximately 20 minutes. Is there an idle fan that I should be checking out for fuses or bad fan or is this a common issue?

And why does the clutch fan engage at engine start up when the engine is only at outside temps?

So much to learn still.

Thanks for any help and I'm glad I found this forum. It's been awesome in helping me out.

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2008 LMM 2500HD
172k miles
ECM mod to the Duramilager
K&N dry intake
Modified hood for cooler temps
Bumper mounted LED light bar
6 tube 120psi train horn
Fusion controller for monitoring and DPF delete with
straight pipe and baffled muffler
Resonator bypass
PCV bypass
2" torsion key lift and 5th wheel rails.

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Old 06-21-2019, 08:27 AM   #2 (permalink)
Rvn4me
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Michigan Oil Burners Member

It’s called “morning sickness”
The fan will often be "on" when you first start the truck. The fluid in the clutch can settle when the engine is hot causing the fan to be on when you first start the truck.
The fan hub has thick fluid, and will be activated until the fluid warms a little.
Even in summer the clutch fan will do this in the morning (after sitting all night) and does the same thing in the winter only for a bit longer..

When was Last both thermostats changed & fluid.

LML and up the fan is controlled by electronics.

Google “Duramax LMM how fan clutch works” lots to read
https://www.dieselplace.com/forum/63...hermostat.html
https://www.dieselplace.com/forum/63...ifference.html


Last edited by Rvn4me; 06-21-2019 at 08:53 AM.
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Old 06-21-2019, 09:42 AM   #3 (permalink)
Jimpa
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Didn't know the fan had fluid and I've never changed a t-stat
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Old 06-21-2019, 09:58 AM   #4 (permalink)
Jimpa
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I have cleaned the stack with low pressure water and an a/c coil cleaner. I have not separated them tho.
I read my temps on my fusion edge instead of factory gauges.
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Old 06-21-2019, 10:18 AM   #5 (permalink)
Jimpa
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This also with the a/c running, haven't tried it with no a/c
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2008 LMM 2500HD
172k miles
ECM mod to the Duramilager
K&N dry intake
Modified hood for cooler temps
Bumper mounted LED light bar
6 tube 120psi train horn
Fusion controller for monitoring and DPF delete with
straight pipe and baffled muffler
Resonator bypass
PCV bypass
2" torsion key lift and 5th wheel rails.

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Old 06-22-2019, 07:55 AM   #6 (permalink)
D_R_C
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What Rvn4me explained in post #2 is one way to know that your fan clutch is working properly even in the summertime when you first start up and start driving.
BUT how well is it functioning after it gets warmed up

In Phx my ECT are usually around 190-195 in stop and go traffic, trans 200-205, in our 105 + temps.

How’s your ac doing keeping your cab cool, is the compressor staying engaged?You can tell by that pretty little amber light on the ac. controls, is the light on all the time or is it off and on until you start driving?
Light on ac clutch is engaged cool air out the vents, light off ac clutch dis-engaged hot air out the vents.
The fan clutch is sealed, so there’s no checking the fluid level.

If everything else mentioned above is working, this very well could be your t-stats.
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Old 06-22-2019, 11:45 AM   #7 (permalink)
Jimpa
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The a/c is fine. It stays engaged all the time, no issue there.
I'm going to do the manual check of the fan today, it seems to be operating normally. It comes on when temp gets high at idle but obviously won't operate until I increase eng rpm or start driving again. No issues in stop and go traffick.

I'm assuming this is normal operation since the fan clutch is mechanical and not electric. I'm also guessing that if I turned the a/c off during long idle that the temps would not increase do to the reduced load on the cooling system.

Does all that sound about right?
__________________
2008 LMM 2500HD
172k miles
ECM mod to the Duramilager
K&N dry intake
Modified hood for cooler temps
Bumper mounted LED light bar
6 tube 120psi train horn
Fusion controller for monitoring and DPF delete with
straight pipe and baffled muffler
Resonator bypass
PCV bypass
2" torsion key lift and 5th wheel rails.

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Old 06-22-2019, 12:17 PM   #8 (permalink)
Ron Nielson
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A couple of thoughts for consideration:

1) The water pump may not be up to the job -at idle. If circulation is poor at idle, it may be sufficient at greater speed. Water pumps do wear out.

2) Have you checked your coolant to be sure you have correct antifreeze to water mix? If you live and drive only in Florida, the number will be different than if you live in Aspen. There isn't just one number that is correct. Too much antifreeze means poor cooling. And when is the last time the cooling system was flushed and new coolant added? You may not know, so this might be a good time to do the t-stats, flush, and new antifreeze.

3) A new GM OEM radiator costs about $350. Other aftermarket radiators are available that advertise increased cooling. Maybe you want to be sure yours is really up to the job.
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Old 06-22-2019, 12:40 PM   #9 (permalink)
Jimpa
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I need to have the system flushed and serviced. I've had the truck since new and it's never been done.

It's the original water pump so it may be getting worn.

The coolant might be off for Arizona, I bought it North Carolina, temps are a bit different there than here.

I'm guessing there is no easy way to check the water pump?
__________________
2008 LMM 2500HD
172k miles
ECM mod to the Duramilager
K&N dry intake
Modified hood for cooler temps
Bumper mounted LED light bar
6 tube 120psi train horn
Fusion controller for monitoring and DPF delete with
straight pipe and baffled muffler
Resonator bypass
PCV bypass
2" torsion key lift and 5th wheel rails.

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Old 06-22-2019, 02:50 PM   #10 (permalink)
Jimpa
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Join Date: Jun 2019
Location: Tucson, AZ
Posts: 48
iTrader Score: 0 reviews

Fan clutch is good.

No leaks on the water pump or lines.

Think I,ll get it flushed and see what happens.

__________________
2008 LMM 2500HD
172k miles
ECM mod to the Duramilager
K&N dry intake
Modified hood for cooler temps
Bumper mounted LED light bar
6 tube 120psi train horn
Fusion controller for monitoring and DPF delete with
straight pipe and baffled muffler
Resonator bypass
PCV bypass
2" torsion key lift and 5th wheel rails.

Offline   Reply With Quote Quick reply to this message
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