Surge Tank Leak at Radiator Cap -- Help!

[lmmargheritis]

Superformance Surge Tank Persistent Leak

I pressure tested my whole system to 19 psi and it held rock steady for an hour and a half. I also removed, tested and replaced the thermostat with a Stant Superstat 180 degree part number 45358. I just returned from a 10 mile drive to get everything up to temperature and this is what I get. Everything I try ends with the same result.

I monitored my temperature and it never got above 195 on the coolant and 205 on the oil temp. (very cool out today) I am running 50% OEM green coolant and 50% water. Boiling point should be way above that.

All I can think of is that the leak occurs at temperature but I can not confirm if it's where the radiator cap tank neck is welded to the surge tank or the primary radiator cap seal on the inside or if it's the seal between the surge tank and the radiator cap. The original cap that came with the tank had a similar issue. The cap that is on the surge tank now is a Stant 10230. 16 psi. When tested the cap actually bypasses to overflow at approx. 14 psi.

The other odd thing is that I am getting coolant moving to and from my overflow tank which should not happen with my temperatures and a 16 PSI radiator cap. I am filling the surge tank to about 2/3 so there should be more than enough space to allow for expansion.

Help Appreciated