Vehicle

Replace the thermostat and see what happens don't work could be the water pump, radiator clogged/defective cap-could be airlock try bleeding it-don't work get it block and pressure tested

I have a few suggestions.
1 some of the V6 water pumps have a plastic impeller that doesn't spin with the shaft.
2 make sure the long tubes that run under each side of the car to get water to the radiator has not been smashed from someone putting it on a lift incorrectly.
3 if you have a leak at the heater core, you need to replace it.

Oh, and PS there is a special bleed procedure for the system.

I have a few suggestions.
1 some of the V6 water pumps have a plastic impeller that doesn't spin with the shaft.
2 make sure the long tubes that run under each side of the car to get water to the radiator has not been smashed from someone putting it on a lift incorrectly.
3 if you have a leak at the heater core, you need to replace it.

Oh, and PS there is a special bleed procedure for the system.