Ok, I know this is dumb (an coming from a diesel tinkerer by trade at that;)
what is the proper cold coolant level? is it at the seam on the reservoir/degass bottle where the arrow points too or on top of the words "coolant level"? I see pictures with it up higher than the seam where the arrow points.

thanks for the help!

I guess this should go in the fluid section.
sorry!

The bottle seam is a starting point. The coolant level should not vary too much.

The seam is the right place when cold but you can make a mark a half inch higher and fill to that so it is easier to see.Both Duramaxes I have owned have gone down on fluid over time,dont know where it goes.

Not a dumb question. My answer will be debated.
I’ve always filled mine to the plastic tab, which is about ½-3/4” above tank mid-seam. More assurance your system will build proper pressure as the warming fluid expands. I’ve never puked fluid out, and after warm-up, the upper rad hose is always very firm, assuring proper pump suction pressure, to assure maximum pump flow.

Link below probably written for a gasser:
http://www.gm-trucks.com/home/content/view/149/25/

Open “canoworms” link below:
http://dieselplace.com/forum/showthread.php?t=49060&highlight=canoworms

I fill min to this level ( 1/2 above seam) and it always seems to be at the seam or lower when I check it. Not sure where it goes either. Can anybody explain?

With our 06 lbz during the last oil change I noticed what lookd like coolant streaks down the back left hand side of the engine block. I was looking because we had used almost a quart of coolant towing on our last trip, approx 2200 or so miles. The dealer said they found two leaks, one line and the other a cooler or heat exchanger or something they were not very specific on the warranty invoice regarding the part. It will probably be going back in for the same thing soon because the coolant level is going down again. The mystery coolant issue seems to be the norm with these engines.

I never fill past the recommended fill line. Filling above the recommended level creates the potential for fresh air to enter the system. Oxygen is bad for Dex and any cooling system in general as it supports corrosion. The fill line location is there for a reason.........