I have a 96 3.1 Lumina.It is overheating and does not have any heat inside the car.The upper rad. hose is hot but the lower hose is cold.Also the heater hoses are cold.I would think if it was the thermostat I would still have heat inside the car.Fluid levels are full in both the rad. and the overflow jug.I suspect the water pump but have never seen a bad impeller or broken shaft.Would appreciate any help.