If its like my 94... it should be in front of the driverside back tire. near the gas tank. :) good luck
For a 1999 Mercury Grand Marquis : ( the engine air filter is Motorcraft FA-1668 )
The cabin air filter, in your 2004 Mercury grand Marquis, is located behind the dashboard on the passenger side. The air filter is directly behind the glove compartment.
Its located on the passenger side before the rear axle in the middle of the rear doors
According to the 2003 Mercury Grand Marquis Owner Guide : With engine oil filter change ( 6.0 quarts / 5.7 liters of engine oil )
According to the 1998 Mercury Grand Marquis Owner Guide ( and one of Fords websites ) The ( Motorcraft FL-820-S ) engine oil filter is used
The 1997 Mercury Grand Marquis owners manual shows : ( Motorcraft FL-820S ) and fordparts.com shows : ( Motorcraft FL-820 ) for the engine oil filter
According to the 2000 Mercury Grand Marquis Owner Guide : The 4.6 liter V8 engine takes the ( Motorcraft FL-820-S ) engine oil filter Also , with engine oil filter change : ( 4.7 liters / 5.0 U.S. quarts of 5W-30 )
( 6 quarts with engine oil filter change ) according to the 2003 Mercury Grand Marquis Owner Guide
According to the 2006 Mercury Grand Marquis Owner Guide : With engine oil filter change : ( 6.0 U.S. quarts / 5.7 litres of 5W-20 engine oil )
It is about 1/2 way between the engine and tank under the car. It is a simple matter of removing it and replacing it.
If it is a 2 cycle engine, it has no oil filter. If it is a 4 cycle engine, the filter is located under the engine cover.
According to the 2002 Mercury Grand Marquis Owner Guide : With engine oil filter change : The 4.6 liter V8 engine takes ( 5.0 U.S. quarts of 5W-20 )