I store my 95 V-12 every year during the winter in my garage. When starting it for the first time getting it ready to drive I checked all the fluid levels etc. and when I opened my radiator cap it still had pressure on it and the coolant overflowed some what. Not a lot but it did come over the rim of the radiator. I topped it off although it only took only about 6 oz. I have noticed this happening if it only sets for a hour or so in the past but should it still have pressure after sitting for over a month. If so what could be causing this and what should I do about it.