[Perfectlap]

There's one thing I have learned about these cars. Do not guess when it comes to anything cooling system related. Have it towed to your local Porsche specialist. He'll charge you $100 and will tell you exactly what is wrong, it could be one thing, it could be several things. Air pockets in your system are a potential disaster. Or maybe he won't charge you at all to diagnose. Either way it's money well spent.

Also, if you have the original coolant cap and removed it to top off, you may be inviting big trouble.
That cap may not be able to hold pressure once removed. It needs to be updated with the most recent version. If you have a leak, and the original cap, the previous owner may done performed a flush and introduced air into the system which may have hairline-cracked the coolant tank. Don't mess with the coolant unless you have the updated cap.

If you do need the new cap, and a new coolant tank then it would probably be a good idea to replace the water pump if you're going to be doing all this. Engine rebuilding experts on this site have posted that if everyone replaced these before they actually failed, he'd have a tiny fraction of cars to work on.