Having problem maintaining water temp after water

Possible clogged engine coolant ports, inspect thermostat for sticking or if installed correctly. Hopefully this helps!!

Air in the system

let the vehicle cool down
removed the radiator cap
block the front wheels
raise the back of the vehicle about 2-3 feet
start the vehicle and watch your coolant
when you start getting a good stream pouring you have "burped" the system

This is either an air lock or a leaking headgasket. Remove the rad cap, with the rad full, watch for air bubbles. You didn't tell us if you were adding coolant??