Same happened to me, but at a stand still. Emptied all of its coolant on a car park. I had the .01 revision cap, and the latest is .04. The seals crack on the older ones, air gets in, water gets out, and someone told me that the car can 'belch' to throw out the water to eradicate the air in the system on its own. Either way, it ends with a huge loss of coolant, whether you like it or not.
I replaced the cap, never had a problem since