Possible coolant tank leak - or can something else cause it?
 

I have some coolant fluid on the bottom of my trunk. I figure the coolant tank is leaking but I can't find any cracks using flashlight and mirror. It only has 30k miles on it.

3 weeks ago the fluid level light came on and I added half a cup of water after pulling over then driving off. I didn't do any venting afterwards or anything (oops). Monday I get home and it gushes water underneath the right rear tire. So I figure it came out through the pressure valve due to my failure to properly add water and vent. Parked it until today and test drove...noticed condensation on the trunk lid then fluid on the trunk floor. But I can't find the source of the leak.

Also - does the coolant level sensor have a gasket or o-ring? I can't find one on the parts - can it leak?

Also I noticed the bleeder valve was up during operation and you could hear gurgling in the tank. Is that normal for it to be up even with the clip horizontal? I could push down on it and close it and the gurgling would stop.

Bet its your tank.

Dry out the trunk and throw some talcum power under the tank. I really could see the crack in my tank until it was removed. It was hairline at best but once under pressure, it doesn't take much.

Purge valve (silver clip) should be down, or horizontal.

But the thing is after I dried it all out I started the car again and went for another drive - it didn't leak. It's not consistent!

IF - you have a hairline crack -it may take 1/2hr of running at normal temperature to build up pressure to cause noticeable leakage.
Remove carpet and use newspaper for leak detection?
Is the cap the old part number(that does not seal correctly after a while)?

It didn't leak driving to work (30 min drive) or to the shop (20 min). They pressure tested and no leak but did find the bleeder valve to be leaky (which I did have condensation). So maybe there was enough condensation to pool together?

Either way tomorrow I get a new bleeder valve and see if that fixes it.