[Halon]

The cap is a 0.9 bar cap. Maybe you are onto something, I will probably grab a new cap to be safe then. See if Stant makes one or something for this car. I see what you're getting at, but on the same note I don't think that the cap is holding in zero pressure, but perhaps it just opened up at some amount of pressure, thus relieving the system of pressure putting it down to 0 once it opened up, then the boiling started and kept going from there.

Thanks for the ideas!