Q: Cooling system hot

I recently purchased an 04 Taurus and recently have had some issues with the cooling system! I drive the vehicle for a little while and the temperature gauge will read hot, so I pull over and slightly open the coolant reservoir and it fills up. A few minutes later, I twist the cap, and all of the coolant goes back down into the engine and the car drives fine with no over heating! Everyday I check the coolant before driving the car and everything is fine, so today, on my way home, the car wasn't hot or anything, and it started clicking loudly, and then died, I was right outside the parking lot of my apartment, so I coasted in and parked her! I got out, opened the reservoir and every bit of coolant came up slowly and loudly. I put a gallon of water in and she turned over, but I didn't test her too much, currently letting her cool off! What could this be and am I completely sunk? Thanks! By the way, I put a brand new thermostat on last week, thinking it might be sticking, not the problem! Again, thanks

My car has 180000 miles.
My car has an automatic transmission.