Need help 2006 LBZ "Low-Coolant" on gauge cluster?

[06LBZCrew4x4]

Hello,
I have a 2006 Chevy Duramax 2500hd LBZ C.C., SB, 4x4 that's pretty much stock. I just got it from my Uncle about 6-7 month's ago, he just bought a new High Country and I flipped my truck leaving his hunting lodge so I finally talked him into selling me this truck. Before I bought it he had it fully serviced because I'm disabled and not working right now. Anyways, about a week or two ago "Low-Coolant" showed up in the information on gauge cluster, I stoped & let it cool down & checked the overflow reservoir & it was low, I added some water that night I topped it off, the next morning before I started it I checked it and it was low. There is no visible signs of Italy key anywhere. The hose isn't hard but is it went you could squeeze it with your hand and I topped it off and it a little bit of driving in the light came on again. I have checked the oil and there's nothing in it, there is nowhere that I can see coolant leak from, I have let it run in my driveway with the AC off and with the AC on and no leaks. I don't know what the problem could be? I guess I am going to take the skid plates off and look at the hoses underneath and make sure there is nothing wrong there. I want to completely flush the system and put new coolant and distilled water in it but don't want to waste the money if it's going to disappear like it has been. I have been doing a lot of reading on here and other places about this and haven't really been able to find out much information. If anybody has had something like this happen in the past or anyone have anything to help me try to figure something out I would appreciate it more than you know. I called the stealership this morning and the service manager said it could be the heater-core, so I'm going to check the carpet today but as much as I wash & vacuum the truck I would think I would have noticed the passenger carpet being wet and I would have smelled something in the truck by now. Any ideas, suggestions, etc.. I would really appreciate it.
PS: I have digital gauges for temp, trans temp, etc. It's always around 180-185 and the transmission is around 150 so it's not running hot, that is something I'm always watching.

 

[oscyjack]

Egr cooler assembly can be the culprit of disappearing coolant and not at all uncommon. It is an item that can be removed if desired, or replaced.

 

[IOWA LLY]

Could easily be the water pump. Look up from the bottom and see if you can see any signs of coolant leaking from the weep hole. Usually the fan and engine heat dries most of the coolant up so you won’t see much of a leak.


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[oscyjack]

^^^

 

[06LBZCrew4x4]

I got a radiator pressure tester and pumped it up 2-3 times and the hose going from the cooler to the motor is leaking. Now it's the fun part of taking all the stuff in the way to replace the hose, then I'm going to do a full flush and run some preston cleaner in it for a few hour's, drain it and see how it looks, run water in it atleast one time, drain it again and hope it's clear.
Question I have now if I get the system completely cleaned where it's clear water, would you put dex-cool in it or since it's completely clean use green antifreeze? If dex-cool how much dex-cool coolant, 100% or 50/50 mix with how much water, from what I've read distled water, Or would you put green antifreeze in it and 100% or 50/50 and qhat water and how much? I've been told to flush it out atleast a cpuple time's and qhen it's clean put 2 gallons of dex-cool 100% antifreeze & 2 gallons of distilled water. I've had other people say if you flush it enough where clear water is coming out to use 2 gallons of green antifreeze and 2 gallons of water?
Thank you all for the help.

 

[06LBZCrew4x4]

I want to remove/block the egr and egr cooler, I'm just not in good health and I don't know if I could do it. I can't find anyone in my area that will do it either, even though I don't like anyone working on my truck.