coolant loss question

[paulb]

I have a new to me this year 2004 Boxster S, recently temps have gotten up over 90 here & I got the coolant low message, the temp gauge reached about vertical (about halfway between 180 & the next line) & the light was blinking. I was close to home so I drove easy & kept an eye on it, within a few blocks the gauge stopped blinking & fell to just over 180. I got home & saw moisture all around the oil & coolant fill/check area in the rear trunk. After everything cooled to room temp I had to add about 1/2 gallon of distilled water & all seemed to be just fine. A few weeks later the same thing happened, another 1/2 gal of distilled H2O, same moisture around the fill area.

I have all the service records for the car & the previous owner replaced the water pump & 1 gal of coolant in '12 (about 7,000 miles ago)

Looking into the problem I believe it to be the cap. My cap is 477.001 version, I've ordered the .004 cap.

The car is stored over winter, so it will not be run in freezing temps. my coolant tester is just the type with little balls that float in an eyedropper & 3 balls out of 5 float which shows protection down to -10.

I was considering just putting on the new cap, adding a bottle of water wetter & calling it done. Water wetter claims to protect from heat better with a lower concentration of coolant (as low as 15% for street & all water for track cars), but does nothing about protection from cold.

Does this sound right or should I be looking deeper? Should I also flush & fill the coolant, to get the proper ratio?