[Ckrikos]

Could be an air pocket or a pinhole in your coolant tank (what color is it?). Does the car run hot? Where does the needle usually rest. If I remember correctly it should be to the left of the zero. Is there any leaking around the water pump? Do you have a lot of condensation in the oil/coolant compartment? Did you check your radiators? They have plastic end tanks that do fail. Sorry, but the 9x6 cooling system sucks across the entire porsche platform.