I have a 1999 Crown Victoria with a 4.6 engine. It was my mother-in-law's and she had never serviced the cooling system. I just replaced the thermostat in it because it kept overheating. Now I have steady stream leaking out of the back of the engine that I cannot find. Please help

 

Wash down the engine to make it easier to find leak. Hard to say if the system will hold pressure if not, you will have to idle it while you look for leaks. Examine the heater hoses, all associated piping and fittings. As you mentioned it has overheated, I would be looking closely at the intake manifold which could have warped, a warped head or damaged head gasket.Check the easy things first.