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i have a 2006 crew cab 4x4 long bed LBZ single rear wheel, I have recently had a problem with overheating as i climb grades towing approx 12000 pound toy hauler it seems to me that the fan clutch isn't coming on unless i use my manual override and drop it into 4 gear at witch time it kicks in and begins to bring the temp down. I've been told by other duramax owners that this is normal operating when towing heavy loads, I have a boost gauge and a egt gauge that i watch faithfully to make sure that turbo doesn't get over 1100 degrees. This truck has brand new head gaskets and a new turbo and is very well taken care of i do not beat it and i've had it since new. Can anyone shed some light on this
 

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I am in the midst of the identical issue on the identical truck (mines a short box)My LBZ overheat thread

My new fan clutch should be here next Tuesday. Going to the dunes for 9 days next Sunday so that will be the big test for me
 

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I am in the midst of the identical issue on the identical truck (mines a short box)My LBZ overheat thread

My new fan clutch should be here next Tuesday. Going to the dunes for 9 days next Sunday so that will be the big test for me
Please keep me posted,we left Parker AZ on the 29 of June we’re in Yellowstone mt as I write this, we have pulled some monster grades on this trip we went thru California on Hwy 101 all the way to ocean Park Washington then across Oregon up to coeur d Alana ID and then across ID and made a right turn and headed south into Yellowstone I think we hit two grades that were close to 10% climb and at least 5 miles long on both of these I was in 3 gear at 30 mph by the time I got to the top and my temp
Meter was an 1/8 inch from the red line . Let me know if your fan clutch helps you out please
 

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When was the last time you cleaned your cooling stack?

 
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If you’re pulling 12k up and around those types of grades, in summer heat, I’d say your truck IS probably in the normal realm. Make sure the stack is clean but other than that, the fan clutch isn’t going to kick in until the coolant temp is up near 230 and the factory gauge is HORRIBLY inaccurate.
 
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And you might consider an auxiliary radiator like from coolertowing dot com. LLYs are notorious for getting too hot, but this solved my problem (and I just have a truck camper in the bed).
 

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I pulled our 7,000 lb camper north here in Michigan yesterday. 88-90 degrees and 60% humidity the whole way. A/C on, 15-20 mph wind (in my face most of the way), running 68-70 mph. On one decently long 7%ish hill, starting speed of 75 mph at the bottom and 68 mph at the top, coolant temp touched off 220 for about a minute. Factory gauge read 210. Factory gauge barely moves when the coolant temp fluctuates between 195-210. Gauge sits just one needle width below 210 during those temps. Let the truck idle at the fuel station for about 5 minutes and the coolant temp drops right to 185 degrees and the gauge will drop to almost the 1/4 mark. I ran 5th gear with tow/haul mode on most of the way. On long downhill sections I would manually shift the trans up to 6th. I got 12 mpg over that 200ish mile run. 1/2 flat, 1/2 rolling hills.
 

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Could always change thermostats as well. Depending on where you live and where your truck is from, it could have a higher temp or lower temp thermostats. I live up north where ots cold most of the year so my tstats open later to keep heat in the engine. On a hot day sitting at lights in town or in a line up she can get pretty toasty.

If you dont have the lower twmp tstats already, they might help a smidge. Definitely look at cleaning the stack though. Just something to think about.
 

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Discussion Starter #9
I pulled our 7,000 lb camper north here in Michigan yesterday. 88-90 degrees and 60% humidity the whole way. A/C on, 15-20 mph wind (in my face most of the way), running 68-70 mph. On one decently long 7%ish hill, starting speed of 75 mph at the bottom and 68 mph at the top, coolant temp touched off 220 for about a minute. Factory gauge read 210. Factory gauge barely moves when the coolant temp fluctuates between 195-210. Gauge sits just one needle width below 210 during those temps. Let the truck idle at the fuel station for about 5 minutes and the coolant temp drops right to 185 degrees and the gauge will drop to almost the 1/4 mark. I ran 5th gear with tow/haul mode on most of the way. On long downhill sections I would manually shift the trans up to 6th. I got 12 mpg over that 200ish mile run. 1/2 flat, 1/2 rolling hills.
I’m wondering what your EGTs were on that run up the hill, I never let mine get over 1200 degrees!!
 

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I’m wondering what your EGTs were on that run up the hill, I never let mine get over 1200 degrees!!
I’m sure they were probably up there but it’s a stock truck with 208,000 on it. I figure if they were too bad, I’d know about it. 😄
 

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My truck used to run hot goin to Colorado haulin my kawasaki mule. Would stay at 220-230 and got up to 245. So bout two years ago I flushed my coolant and replaced both t-stats. And didn’t quite fix the prob. So the next year I cleaned cooling stack and replaced fan clutch. Then took a trip to Colorado runnin bout 80-90mph and the temp got up to 230 just a couple times but dropped quickly. But since I cleaned everything and new clutch. My normal drivin temps r bout 180-190. Hardly ever gets up to 210 unless towing. (I have an edge monitor)
 

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Clean your cooling stack. Not from the outside, but by following the procedures for pulling your grill out, separating the stack and cleaning each radiator/cooler. I struggled with this for months, and pressure washed the stack. That didn't work. Took the stack apart, cleaned it right and the problem immediately went away.
 

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i have a 2006 crew cab 4x4 long bed LBZ single rear wheel, I have recently had a problem with overheating as i climb grades towing approx 12000 pound toy hauler it seems to me that the fan clutch isn't coming on unless i use my manual override and drop it into 4 gear at witch time it kicks in and begins to bring the temp down. I've been told by other duramax owners that this is normal operating when towing heavy loads, I have a boost gauge and a egt gauge that i watch faithfully to make sure that turbo doesn't get over 1100 degrees. This truck has brand new head gaskets and a new turbo and is very well taken care of i do not beat it and i've had it since new. Can anyone shed some light on this
What temps are you seeing? Is the vehicle stock? How many miles?
 

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We have a 2003 2500 HD Silverado, Duramax/Allison with 147,000 miles on it. Pardon me for being dumb, but what is the cooling stack and where is it. I am a woman! lol
 

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Coolertowing.com. I owned a LLY 05 Duramax. First time towing my 14K toy hauler up Interstate17 to Flagstaff from Phoenix in the middle summer was a learning experience. I over heated multiple times and had stop to allow the truck to cool down from over heating. I contacted Joe at Coolertowing.com. Had the exact same truck as I, and explained he had the same exact issue of over heating when towing heavy. He showed me his truck and explained about an engineer flaw of our trucks of how air flowed over and under the stack, (radiator opening for air flow) instead of through the openings. Simple fix, add an auxiliary radiator in front and sightly below the main radiator, plumbed with all the parts necessary for a clean install. Problem solved with additional fluid cooling capacity towing, keeping temps well below the activation for the clutch fan to activate causing a strain on the engine. Money well spent
 

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We have a 2003 2500 HD Silverado, Duramax/Allison with 147,000 miles on it. Pardon me for being dumb, but what is the cooling stack and where is it. I am a woman! lol
The cooling stack is made up of the radiator, AC Condenser and Intercooler, all "stacked" one behind the other in the front of yoru engine.

All sorts of debris builds up between the individual parts and prevents a good airflow. Since the radiator is in the back the engine overheats due to lack of airflow
 
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