Make sure you have the latest coolant tank cap ending in P/N 04. Could be the cause of coolant leaking down and underneath the coolant tank. Looks like a good project so far!

 

Indeed, I don't have the new cap ending in 04. Spent 4 hours last night putting the SC back on, etc... only to still see a leak this morning, after a drive. At least this time, I can plainly see the origin of the leak (change quality to 720HD for better viewing)

I've contacted my indy mechanic who put this in to see if the part can be returned under warranty.

Looks like I'll be taking the SC off again!

I suppose another option would be to plastic weld the leak. From the research I've done, I believe the plastic is polyethelene.

 

I'm shocked that that leak didn't show up under a 25PSI pressure test. WTF? I feel for you. That tank is a total bitch to remove and install. Wanted to heave mine across the garage when I finally got it out.

To KK, I agree, I don't think the sensor uses temperature for level, as there is no way for it to know "what" temperature is valid. I am curious if anyone knows how it does work. I assumed it was magnetic reed switch, and there was a captured magnetic float, but to be honest, when I had mine out, I don't recall seeing anything like that when I flushed it out.

 

Unfortunately the OP only relied on pulling vacuum to verify leak. Vacuum is only ~14 PSI so not enough to open the crack. Also, vacuum is not a good way to verify leak because when the tank leaks, it's the positive pressure, about 2 bars that "pushes" open the crack which vacuum test can never duplicate.

 

I thought twice about putting that tank back in, with just a vacuum test. I should have rigged something up and used my air compressor. Lesson learned...

 

Even that may not be enough though since some tanks leak only when they heat up (by the coolant) so only an in-car test will be the most accurate.

Anyways, the bright side is now you're 100% sure the tank is leaking so you won't feel bad spending the money on a new tank. Some tanks leak such that they weep and drop the coolant on the exhaust so the coolant just disappear w/o a trace. Almost impossible to trace visually.