I would asume it came from the factory with ( 5W-30 ) like my 1991 Ford
Mustang 5.0 liter V8 engine did
134 a
For a 1999 Mercury Grand Marquis : ( the engine air filter is Motorcraft FA-1668 )
According to the 1997 Mercury Grand Marquis Owner Guide : ( 5W-30 ) is the PREFERRED oil
Disc, front and rear.
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
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 )
It takes R-134a. Good luck.
According to the 1999 Mercury Grand Marquis Owner Guide ( and one of Ford's websites ) ( Motorcraft FL-820-S , engine oil filter )
mercury marquisA 1993 Grand Prix
A 1994 Mercury Grand Marquis would have come from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze ( meeting Ford specification ESE-M97B44-A )
According to the 1999 Mercury Grand Marquis Owner Guide : ( 5W-30 engine oil , certified for gasoline engines ) With engine oil filter change ( 4.7 litres / 5.0 U.S. quarts )