[rick3000]

Yes, under normal circumstances you should not have to top off the coolant. If you are using Porsche coolant it leaves a white residue to help identify the leak. The most common issues are a bad coolant cap or cracked tank. Feel around under the carpet in the trunk, and pry the plastic cover under the cap off and check the bleeder valve. Also, if you have already topped up with 16oz of water you may want to start using a 50/50 mix. However, if you do not know what is in the system do not add a random coolant, mixing different coolants can cause them to congeal.