Ok serious newbie here... I've got a big coolant /water leak underneath that when radiator cap is removed to it becomes a gushing/pouring leak. Hose? Why would cap effect leak if it is indeed a loose or damaged hose?
Basic physics. When the cap is off, air can enter through that big hole. when the cap is on, air can only enter through the smaller hole where you have the leak. The leaking coolant has to be displaced by air.
