A crack near or on the thermostat housing can cause a coolant leak in a 1996 Grand Marquis. The thermostat housing is located near the manifold on this vehicle.
what is it leaking? water, oil,coolant,or gas
lack of coolant, check for leaks.
better have the head gasket checked for leaks
thermostat sticking or low oil or low coolant
change your antifreeze fill cap.
You would pour it in the radiator. Caution, stop leaks usually clogs heater cores.
How To Find & Fix Coolant Leaks http://www.aa1car.com/library/coolant_leaks.htm
Diesel Grand Vitara engine problems can be caused by low-quality oil or coolant leaks. Fouled spark plugs can also cause the problems.
3.1 engine leaks at the intake gasket
Probably the thermostat is sticking.
Most often that indicates the presence of water or coolant in the combustion chambers. Common causes are head gasket leaks, intake gasket leaks, warped head/s or warped intake.
THe reassembly didn't go well. A failed seal, a cracked hose or similar.