ha. yes. i've had the same issue for a couple years. topped off and it never goes above min with no fluid seen anywhere. none in the engine either I assume there is a slow leak from the reservoir and will replace this year.
you're not alone in thinking you're crazy.

 

For those who replaced their expansion tanks, how much coolant did you need to add after installation? I'll be doing this soon and don't want to under/over buy coolant.

 

I wished I asked too before buying, but I decided I would change all the coolant when I change the container so it's like a once every 12 years maintenance item.

 

I am noticing a coolant smell after driving. I can see on my expansion tank, there is a faint line where the tank tends to crack. That said, there is no residue of old coolant on the outside of the tank. Could a hairline crack cause a smell without leaving behind coolant residue? I don't see any coolant residue anywhere else on the cooling system (water pump weep hole, etc)

 

Put a pressure tester on the system at 16 psi and locate the leak.

 

The coolant level has not changed during my ownership. There is no visible leak, no evidence of past leaks, only a smell. Pressurizing to 16psi happens with every drive, and still does not force any coolant out. Perhaps I will try some soapy water on the crack (which looks to be about 10% as progressed as the ones pictured above) next time it's warmed up.

My question remains for the folks who have had the seemingly common coolant tank crack; would that crack allow for a smell, without any visible residue or actual coolant loss?

Also, has anyone had luck with a non-porsche part for replacement being a better alternative? I see a few other options, cheaper to boot, since the oem one doesn't seem so great anyways.

 

2009 C2S 180K miles

A common failure of the coolant tank is the blue cap. To see if it is leaking, unscrew and check for residue around the threads etc. Mine did a few years ago. Also check the "bleed valve", the cap next to the blue cap, for any residue. They are relatively cheap replacement costs.

On my tank, original with 180K miles on it, I have a stress mark (not a crack yet) where everyone else sees a crack leak. I have no leak. I was tempted to change out based on that line, but I like to do some "science" and see how much life I can get from this tank. There is a bit of a danger as if it splits real good, you are stranded... but that does not appear to be an issue with these tanks... they dribble before they fail big. Not so with my 2000 Boxster S where the tank decided to split on the hottest day in the summer and left we stranded two hours from home. I suspect the bleed valve did not vent off the pressure ... maybe. I went through at least three, maybe four tanks on that Boxster in 197K miles of ownership.

Peace
Bruce in Philly (now Atlanta)