I have a 1999 lincoln towncar that is overheating and I don, t know why. It has the 4.6 liter with about 72,000 miles on it. I thought it was the thermostat, so I replaced it, then the thermostat seemed to be sticking, so I took it out and ran the car without a thermostat. When I squeeze the upper radiator hose at start up, it seems like the coolant is circulating, however very shortly afterthat, the hose is tight like the coolant is not going anywhere. Do I need to replace the water pump? Thank you so much.