[Medicone]

I don't know what your normal operating temperature is supposed to be on the 6.0, but if you have 170 thermostats I imagine that running under 180 cruise/WOT would be considered to be within normal limits.  On my 8.1Ls, under 180 is normal.  I just replaced both oil coolers and heat exchangers on my boat (the buyer should be very happy) and it runs comfortably below 180.

Some things to keep in mind:
-the coolant in the degas bottle fluctuates with temperature.  When the engine cools, it should suck some of the coolant out of the degas into the engine.  Check the operating manual for the proper procedure for adding coolant to the appropriate level.  The procedure for my 8.1 is different than your 6.0 because coolant is added initially to the heat exchanger, and then subsequently to the degas bottle.  I don't think the 6.0 has a coolant fill in the heat exchanger - just the degas bottle.
-when you drain/change the coolant, you should flush it a few times to get any sludge out and make sure you are using the same coolant (e.g., GM approved w/Dexcool for my 8.1Ls - usually pink or orange'ish).  You can't mix the green stuff with the dexcool or it will gum everything up
-after you add the coolant, you have the burp the system to get any air bubbles out (see operating manual).
-if you have sludge (make sure it is not oil), I have been told that you can run "Cooling System Cleaner Restore Plus" through it which will clean everything out
-if you see temperatures creeping up, it often is a raw water issue.  A lot of gunk/growth gets caught up at the oil coolers and the heat exchanger raw water sides.  I would check the inspection ports on your heat exchangers/flush out the tubes with fresh water as well as backflush the raw water side through the oil coolers.  It's interesting to see what comes out.
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