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Great post. I used this to replace my 2 coolant thermostats in my 2007.5 Chevy 2500HD. See attached pictures. Hope this helps anyone.
 

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When I replaced mine the first time I used the cooler temp stats. I had a cooling problem in the radiator stack but wasn't aware of it at the time. the engine never came up to proper operating temp so the computer read cold engine and my milage really went in the crapper. Changed back to the normal stats and motor ran much better. Cleaned the cooling stack and everything was golden. I got OEM stats over aftermarket and they have performed flawlessly.
 

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My 2006 LBZ has no radiator drain plug so the easiest way is to remove the passenger side inner wheel well. This is easy to do and makes the entire job easier. Just remove the plastic push pin fasteners and a couple of bolts on the lower front of the wheel well. Push the wire loom fasteners back through the plastic inner wheel well and then the wheel well slides out.
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To drain the antifreeze the engine must be cool. First relieve the pressure from the cooling system by loosening the radiator reservoir cap and then re-tighten. Remove the clip where the lower radiator hose attaches to the radiator. This quick connect eliminates the need to remove the clamp on the actual rubber radiator hose.
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With a bucket beneath the hose, pull out on the hose slightly to let the antifreeze come out slowly. The rate of flow can be controlled by loosening or tightening the reservoir cap to lessen the mess created by the antifreeze. My truck had 133k miles so I decided to drain all of the coolant out and replace it. Don't reinstall the radiator hose back in place until the job is finished. It will make the next steps easier with the hose being able to be moved. Remove the turbo noise suppressor on the top of the motor with a Torx T30 bit and also the hose clamp. Cover the intake hole with a rag.
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I chose to move the air compressor to have easier access to the thermostat housing. It can be moved without disconnecting the A/C lines. To gain access to my serpentine belt tensioner, the upper radiator cover and fan guard both needed to be moved. To gain access to the radiator cover fasteners, I found it easier to remove the air cleaner. Remove this little plastic cover that is snapped into place.
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Unplug the air flow sensor and loosen the hose clamp and the entire unit lifted out with just a little manipulation.
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There are no bolts holding it in. Only these little posts on the bottom side of the filter housing.
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Next remove the two bolts on top of the upper radiator cover and remove the push pin fasteners about midway down the radiator. I assume that there are normally two fasteners on each side but mine only had one on the passenger side.
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On the drivers side, the Transmission Control Module is attached to the radiator cover. There is a slide lock on the plug on the bottom. I could not see it so I just left it commnnected. There is enough slack in the line to just lay the radiator cover off to the side while still connected.
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There are three bolts holding the fan guard in place. Loosen the lower bolt on the passenger side near the lower radiator hose that was left disconnected. I was able to leave this bolt attached but very loose. Remove the top fan guard bolt near the oil fill tube. I had no problem with leaving the driver's side bolt completely tight. the guard only needs to be moved out enough for the wrench to adjust the belt tensioner.
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Use 1/2" breaker bar on the belt tensioner to remove the serpentine belt from the A/C compressor pulley. Remove the two electrical plugs from the compressor and the one electrical plug from the thermostat housing.
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Remove the four bolts holding the compressor in place and the compressor can be flipped up and out of the way towards the passenger side of the engine.
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Next remove the two oil fill tube bolts. Try to clean any dirt from around the tube to motor insertion point as the tube is pulled out to minimize any dirt getting into the hole.
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Cover the hole with a rag so no dirt or antifreeze enters when the thermostat housing is removed. Remove wire loom bracket attached to the top of the thermostat housing. Remove the bolt attaching the black coolant tube to the thermostat housing. Remove the four thermostat housing bolts. I did not loosen any of the other bolts holding the black coolant tube in place. I lifted up on the housing to break free the seal of the thermostats.
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The front thermostat did stick to the housing cover which inhibited the removal of the cover. I used a screw driver to pop it out of the stuck gasket back into it's seat to allow the cover to be removed.
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A bit of wiggling back and forth will remove the housing from the black coolant pipe. Clean both surfaces really good. I lightly used 220 grit emery cloth to clean the mating surface of the housing cover. Installed the new o-ring on the outlet pipe and used dielectric grease to make installation on the pipe easier.
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The thermostat with the jiggle pins must go towards the back of the motor with the jiggle pins located towards the back of the motor.
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This thermostat is made off center to allow for the sloped shape in the back of the hole on the engine. Installation in any other position other than this can cause the lower part of the thermostat to bottom out before resting in the seat.
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Install housing on black outlet pipe. Install all four housing bolts and the outlet pipe bolt loosely before tightening them all. Torque the four housing bolts to 18 ft/lbs. Install new o-ring on the oil fill tube and install tube. Lay compressor back in place and install bolts. Don't forget that there is a wire loom bracket that is attached with the rear passenger side compressor bolt. Torque compressor bolts to 37 ft/lbs. Install wire loom bracket on to the thermostat housing. Plug in the two compressor electrical plugs and the thermostat electrical plug. Reinstall serpentine belt. Reinstall bolts and tighten on the fan guard. Reinstall radiator cover. Install air cleaner housing and tighten clamp. Plug in air flow sensor. Reinstall lower radiator hose and clip. Remove the coolant bleeder plug on the thermostat housing.
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Tuck rags around the housing for any overflow when filling radiator. Fill through the reservoir until coolant comes out of the bleed hole. Install the bolt in the bleed hole. Clean spilled coolant to keep it off the belts. Top off reservoir to proper level. Run engine to check for leaks. Leave wheel well cover off until after running engine to get good circulation so any leaks can be spotted easily.
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Nice post. (y)
But to add to it, for others that follow....once you remove the air box and the pass side inner fender liner, if you also go ahead and remove the air box shelf and bracket, that will give you room to access (thru the fender well) the drive belt tensioner to release, without messing with the engine mounted fan cage. But the cage is only 3 bolts, so it's no big deal there either.
 

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That's good to know for the future. Does that apply for the classic body style? That's what I own. Lol. I just noticed that my profile still lists my previous 2002 truck that was totaled instead of my present 2006. I need to change that.
 

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'01 - '07 are all considered 'classic' body styles. In an attempt to deal with the LLY overheat issues, the engine mount fan cage (along with a larger rad) was added to the LBZs in '06, to enhance the air flow from the fan.
 

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Thank you for sharing the step by step procedure, I will try to check if it is time for my truck to undergo thermostat replacement.
 
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