19 gallons, but it only gets 18 MPG.
I found this info out on DriverSide.com, you can find more specs there for other cars.
On a 2001 Mercury Grand Marquis : The fuel tank is mounted vertically behind the rear seat
According to my Chilton's Auto Repair manual : A 1988 Mercury Grand Marquis has a ( 20 U.S. gallon ) gas tank
12 Gallons (US)
As much as the gas tank will hold... ---------------------------------------------------------------------------------------------- On a 1997 Mercury Grand Marquis , the gas tank capacity is ( 20.0 U.S. gallons )
My manual says fuel tank capacity is 19.0 gallons (71.9L).
In the fuel tank.
According to the 1999 Mercury Grand Marquis Owner Guide : ( 71.9 liters / 19.0 U.S. gallons )
According to the 2003 Mercury Grand Marquis Owner Guide : ( 71.9 liters / 19.0 U.S. gallons )
According to the 2000 Mercury Grand Marquis Owner Guide : ( The gas tank capacity is 19.0 U.S. gallons )
On a 2001 Mercury Grand Marquis the electric fuel pump is INSIDE the fuel tank The fuel tank is mounted vertically just behind the rear wheels and the fuel pump is mounted high on the side of the tank facing towards the front of the vehicle
On a 2001 Mercury Grand Marquis : The electric fuel pump is INSIDE the gas tank ( it is a vertical gas tank located behind the rear seat and the fuel pump is near the top on the side facing towards the rear seat )
According to the 2003 Mercury Grand Marquis Owner Guide : The fuel tank capacity is ( 19.0 U.S. gallons )