[rick3000]

Check the trunk for coolant, if you find any (the OEM Porsche coolant leaves a white residue) your tank is probably cracked.

If not, the most common cause if an air bubble in the system or a bad cap, as mentioned above. Both of those can cause the coolant to drain from the overflow (located above the rear passenger wheel). Take a flathead and remove the plastic trim below the oil and coolant caps, then flip the coolant bleed valve open. Run it for a day or two with the valve open to purge any air bubbles, especially if you are topping off with water and coolant to replace what leaked.