2007 Classic Duramax.........Today I noticed coolant leaking on the ground under the truck. I opened the hood and see it coming from the big pipe, intercooler I believe above the engine on the drivers side. Is there supposed to be coolant in there?
It's not possible for coolant interaction at the hot side pipe on the driver's side.
There is a potential hose leak area just below that (and the main harness), that could spray up, leaving a coolant residue to drip from that you see. That short piece of hose is on the coolant return line from the turbo.
Look at your top rad hose and the pipe it connects to, next to the main harnesses.
Item #7 below is the valve on the coolant return line from the Turbo.
If you follow that T line, down under the main harnesses, you'll see a short 3-4" section of hose between the metal lines. Full of coolant and at OP temps, view that area and see if it's your leak source.
Here's another exploded view of the Turbo coolant line routing. Item #120 is the hose.
(bulk coolant line will work for replacement).