[linkjones]

Might be a leaky resevoir. I'm experiencing the same problem but haven't done anything about it yet as I just parked mine for the winter, you can order the resevoir from ************************************************************ for about $500 but you may want to check your connection hoses on the side. While you're at it you may want to replace your coolant level sensor as they can get gunked up, it's about $30. It goes on the bottom of the resevoir.

Zerex makes an acceptable coolant that is approved by Porsche, I don't know the name of it off the top of my head but if you do some research you'll be able to find it.

This seems to be a common problem, let us know if you get it resolved.