I had posted recently that after replacing everything on my cooling system, I had forgotten to SCREW THE CAP DOWN ALL THE WAY!!! Otherwise, even if temps are normal (which they were for my situation as well), the lack of pressure lowered the boiling point, and forced the coolant through the cap (which wasn't tightened down anyway).
This may be obvious to most, but I struggled with this for about two weeks before I figured it out...DUH!
