during warm up,it pushes antifreeze into the ovrflow tank'temp gauge goes to hot on 2004 Mercury Mountaineer

then wwhen the thermostat opens it sucks the antifreeze back in and it's fine untill the engines cold ,then it does it again ! New thewrmostat, antifeeze ,fushed hearter core engine & rad ,! IS water pump bad,rad pluged? Pressure checked holds 16 lbs

Asked by for the 2004 Mercury Mountaineer
New radiator cap?