Alright trivia problem here, please help. My 2008 Edge overheated, was very low on fluid in radiator. We added water. It overheats when driving. I turn it off, it cools down and water sounds gurgle. If I turn on the heater, it blows cold, but then warm and car will cool down. Drive a little ways, it overheats again. So I am thinking maybe thermostat stuck and water pump is bad, or did heater core go out? What ways can I tell?

Please give me solid ideas and opinions.

Thanks