OMG What just happened?

[coreseller]

The guy I bought my Boxster from had a similiar episode after topping off the coolant. He freaked and shut the car down and had it towed to the dealership, it turned out the cap was not on correctly. One of the reasons I bought the car from him, VERY cautious.

[Lil bastard]

It's probably not a bad idea to run the car at isdle for a few minutes with the coolant bleed valve open. This valves is under the plate that the coolant and oil fill pipes (they stick through it). Pull both caps and then with a screwdriver, pry up the plate. You'll see the valve, lift up on it to open it, then let it run 5 min. or so, revving occaisionally to force any air through the system to the valve. As the coolant warms, you'll get a little overflow, so be prepared with towels, etc. to keep it out of the trunk. Close valve and replace plate and caps. Run it a day or 2 and then recheck the coolant level.

IMHO, it's probabl;y good to always have the valve open when you add coolant to prevent this, also, it's better to add coolant with the engine running, not Hot of course, but before it heats up.