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Discussion Starter #1
My friend is helping me move some stuff around in their 2012 Chevrolet 1500 V8 4X4 with like 400k miles on it. About half that mileage was in-tow behind a larger truck, so its still all original drivetrain.

There is a bad valve tap on the right bank, possible exhaust manifold crack, and Dexcool consumption through the motor that requires constant topping off for proper thermostat functioning. Heavy acceleration, which we try to avoid, causes the exhaust to smoke white and has recently also been accompanied by a Stabilitrack/Safe-Mode alert kicking in.

Does anyone have suggestions based on similar experiences or general knowledge about these trucks? Of the many motor-glue type products available, can anyone refer a block/gasket sealer for the coolant here?

The electronic 4x4 engagement, or disengagement more specifically, has been tricky. It was suggested at the parts store that this could be a $400 electronic actuator mechanism that piggybacks the transfer case. Any general advice here would be helpful, along with comments on the hypothesis that this is causing the Stabilitrack to go haywire.

I am going to repay the favor today by replacing the tailpipe and changing the oil, so please let me know what I should also try to look into further.

Thanks in advance!
 

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On the 4x4 engagement problem you might try pulling the fuse for it and replacing it. I had an 04 that did that. At first I thought it was blowing the fuse and I had replaced it several times which allowed me to move in and out of 4 wheel drive. Then I realized that the fuses weren't actually blown and that just pulling them and replacing them was resetting something in the system. I ran it like that for a couple of years. Back then I was still living on my hobby farm and used the 4x4 often.
 

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Discussion Starter #3
I'll look into that today.

We're in W. Frederick Highlands, so its all steep icy inner city asphalt right now.

Thanks.
 

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The lifter tapping, with service stabilitrac could be a serious issue, especially if the truck is equipped with DOD/AFM. It could mean lifter failure with that system, which is fairly common especially considering the mileage on it. A manifold cracking wouldn't be surprising.. The coolant leak could be a few things. Most common that I've seen is the little H tube that goes across the top of the engine under the intake, on top of the plenum, water pump, or bad head gasket. If you're seeing white out the exhaust, it could be head gasket, or head.
 

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tapping could be broken ex manifold bolts.they are torque'd at 18 ft lbs why the heck they break is beyond me.it will 99% of the time be an end bolt.i have had 3 different suburbans a yukon and an express van and they have all had at least 1 broken bolt.also as mentioned the afm system can be a pain,
 

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On my 04 there is 3 ground wires that are attaches to the frame body mount right below the drivers door this is where the tcm gets its ground from.
White smoke out of the exhaust is more than likely internal head or head gasket.
 

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I know its hard to diag a problem online.here are my thoughts.Possible front axle accuator,its screwed into the axle houseing.encoder motor possible to.Check dtcs and you will have some codes set.This will point you in the right direction,I ve seen hose clamps break and cause coolant loss to.
 

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on my 2002 1500 HD, I had two exhaust manifold bolts break and no exhaust leak or noises from there. Lifter problems were known to happen on these engines. If it were my truck, a used engine would be going in and as mentioned above, get the codes for the other problems. I put over 150,000 miles on my truck with only rusted out brake lines. I did lived and worked on the DC area for the whole time I drove/owned that truck. Good luck!!
 

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Discussion Starter #9
All these tips are very helpful. Now I have a nice troubleshooting checklist to move forward from. Thanks a lot everyone!
 

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If you are going through coolant and white smoke it sounds like a head gasket. Not good. Is the oil milky?à
 
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