have a 03 C4S,coolant level goes down slowly,cant see any leaks,had a good indy do a pressure test and he cant see anything,no sign of water in oil,any ideas?/

Thanks
Albert

 

How long does it take and how much are you losing over that period.

I have the same issue... I lose about 200 ml every 30 to 45 days. There is no evidence of any loss visually. I am of the opinion that perhaps the heater core is leaking. There is an occasional whiff of coolant when I turn on the A/C after the car has not been driven in a couple of days.

 

Your coolant tank or cap is often the culprit especially if your tank has yellowed, it can develop tiny cracks that can be hard to detect. My tank was leaking for awhile before I replaced it. My Porsche is a MY99 so it's 4 years older than yours. GL

 

Update coolant cap. The newest version ends with "04."

 

If I fill mine up to the max it will always go back down below min and stay there. If I fill it to min it will go back down to where it was prior and stay there.

It's stayed there for 2 or more years so I think the min/max marks are way off.

 

probably loss a quart after 3000-4000 miles,i updated the cap,i guess i will just keep a eye on it and see what happens

 

It is your cap. I had the exact same issue on my 997. New cap solved it.

 

Stevens Creek found the same problem with my cap. They pressure tested it and said it was fine but that the cap was leaking. Actually, there was crusted coolant around the edge of the cap when I got it. I had a replacement in hand when the car arrived. I'm hoping that it solved the problem.

-Eric