Ever since swapping to the Canton expansion tank after the OEM one split, I've been having a bit of coolant weeping from the side of the Canton tank every so often. The 20PSI Stant Lev-R-Vent Cap (part #10335) is what I went with for a cap. Car never overheats or has any issues other than noticing quite a bit of coolant on the side of the tank every few weeks (particularly after some hard driving).

I've checked the forums and the info is split 50/50. Mini recommends 16psi caps for the closed system. Canton, to include other aftermarket tank manufacturers, recommend 30psi caps for their tanks.

Which is correct? I'm under the impression the system is not pressurized correctly causing the weeping. Tank is not overfilled.

 

This is the one I use, never had a problem

 

I had a bit of weeping with the Forge tank and I still have some with the RMW/Canton and Stant cap one.