134 a
A 1998 Mercury would use R134a refrigerant.
R134
R134a
r-12 unless its been retrofitted
For a 1999 Mercury Grand Marquis : ( the engine air filter is Motorcraft FA-1668 )
I would asume it came from the factory with ( 5W-30 ) like my 1991 Ford Mustang 5.0 liter V8 engine did
Disc, front and rear.
According to the 1997 Mercury Grand Marquis Owner Guide : ( 5W-30 ) is the PREFERRED oil
It takes R-134a. Good luck.
A 1999 Mercury Grand Marquis came from the factory with a 50 / 50 mix of distilled water and ( GREEN color antifreeze , meeting Ford specification ESE-M97B44-A )
According to the 1996 Mercury Grand Marquis Owner Guide : ( 5W-30 is the PREFERRED engine oil weight )
According to the 1996 Mercury Grand Marquis owners manual ( 5W-30 engine oil ) is the PREFERRED oil weight