R134a
According to the 2003 Mercury Grand Marquis Owner Guide : ( " regular " unleaded gasoline , 87 octane )
R-134a
It is R134a. If it is serviced, DO NOT use any with leak stop as that will ruin a repair shops equipment.
There should be a sticker under the hood somewhere that tells you how much R134a freon and how must oil the system calls for.
Use a 1999 grand marquis gs key!!
According to the 2003 Mercury Grand Marquis Owner Guide : It came from the factory with a 50 / 50 mix of distilled water and Motorcraft Premium Gold Engine Coolant ( that's YELLOW color , meeting Ford specification WSS-M97B51-A1 )
5w-30 is what I use in my 2000 grand marquis, in 2001 ford started saying 5w-20.
D.
It is important to have the right types of fluids in a car for it to run smoothly. A Grand Marquis will use engine oil 5w-20 or 5w-30.
According to the 2004 Mercury Grand Marquis Owner Guide : ( " regular " unleaded gasoline , 87 octane )
For a 1991 Mercury Grand Marquis : " regular " unleaded gasoline , 87 octane is used for both the 5.0 and 5.8
Use the key or remote.