i believe under car rear section near gas tank.usually a silver or blk. canister.but under high presure.
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.
According to the 2004 Mercury Grand Marquis Owner Guide : With engine oil filter change : ( 6.0 U.S. quarts of 5W-20 )
According to the 2004 Mercury Grand Marquis Owner Guide : With engine oil filter change : ( 6 quarts )
headlight relay location on a 2004 mercury grand marquis
2004 mercury grand marquis fan stop working
According to the 2004 Mercury Grand Marquis Owner Guide : ( 19.0 US. gallons )
On a 2004 Mercury Grand Marquis : firewall 4 - 8 3 - 7 2 - 6 1 - 5 front of vehicle
According to the 2004 Mercury Grand Marquis Owner Guide : ( " regular " unleaded gasoline , 87 octane )
One in the trans and there may be a filter on the cooler line if it had a trans replaced at the dealer or had a dealer reman installed.
Take it to a repair shop.
According to the 2004 Mercury Grand Marquis Owner Guide : The engine cooling system capacity is ( 18 liters / 19 U.S. quarts ) It came from the factory with a 50 / 50 mix of antifreeze and distilled water
Should be 4x6. 3x5 is the other size.