Why would a 92 Eclipse push water back through the thermostat housing and overheat?

The thermostat is most likely stuck in the closed position and needs to be replaced. The closed thermostat does not allow the coolant to circulate through the radiator, thus overheating the engine. The reason for water being pushed through the thermostat housing is because the water pump is spinning and there is no place for the coolant to go, therefore, it is leaking out through the housing gasket which is probably already blown (need to replace it when you replace the thermostat.