[Steve Tinker]

Yes.

The cap is probably leaking - when the coolant cools the leaking cap allows air into the system. When you restart the car, the air expands and forced coolant out through the overflow - which is what you have.

1) Replace cap as suggested above.
2) Top up coolant with distilled water / Porsche coolant 50/50 mix.
3) Open the purge valve D shaped lever for at least 3 x heat cycles of the engine or for a few days. This allows air to be expelled.
4) Top up the coolant tank each morning as the level will drop as air is expelled.
5) If the air is getting to the system because your tank is cracked, you will see moisture under the carpet in the boot.