New Developments. The plot thickens...
 

So when i have the thermostat at 70 or above, i hear a waterfall sound behind the dash. at 65 i hear no waterfall sound.

i only here my water fall sound at low revs on a cold start, but apparently what you describe with water behind the dash requires you to burp your cooling system. plenty of topics on that at hand.

Yep. Burp that puppy.

away i burp!

(but i'm loosing coolant too)

oh i read that wrong with the no sound at 60 but i would still do that, as for loss of fluid.. is there any visible leaks? how fast do you lose it? any over heating?

No leaks, no overheating, I lose coolant verrry slowly.

hate to jump the gun, but any signs of BHG? that could eat it away slowly...

I thought about that. No white smoke, no overheating, changed the oil three months ago, nothing wierd about it then. I'll be changing it next week though.

place an empty container on the coolant reservoir drain hose and drive it like usual....after a long drive check to see if there is coolant in the container...If so..then you most likely have a BHG leaking into a water jacket...{like usual}
this causes high presure in the coolant system pushing the coolant out trhough the reservoir and spilling "only" when the vehicle is driven or at high RPM..

Could it be as simple as your radiator drain plug is not tightend all the way closed???