As noted above, we need to know the engine you have, and the year of the car. If its a 96-99 Vulcan, I would suspect the water pump impeller has corroded its vanes off and is not pumping much coolant, as also noted above.
What brand thermostat was used? I have seen cheapo ones bad out of the box several times. Use ONLY a Motorcraft thermostat.
05 Taurus SEL Duratec - my daily driver
04 Taurus SES Duratec - wifes car
95 Taurus GL Vulcan winter car
Toy #1 - 86 Tbird 5.0 (original owner) - LOTS of mods
Toy #2 - 88 Tbird Turbo Coupe - LOTS of mods
02 Pontiac Grand Prix GT
67 Honda 450 Super Sport - completely customized