coolant
 

This is more of an update on the coolant issue. To recap, drained the system, flushed with distilled water and finally refilled. Had problems with that, even bought a vacuum pump to make it happen. Finally discovered the problem. Reservoir tank leaks. Very tiny drip, but enough to mess it up. Cannot really see from where (not hoses). Will remove it, see if repairable or buy a new one. It's always the little things that mess up a project.

Whatever you do, buy an OE tank. It's too much hassle and work to put an aftermarket unit in there. :)

The coolant tanks on the 986 are prone to breaking so glad you tracked down your culprit. Porsche has redesigned this part several times, but they still have their issues. If you need help and want more info please check out this article here: Porsche Boxster Coolant Tank Replacement - 986 / 987 (1997-08) - Pelican Parts Technical Article.