Original is 16 inch with 225/60 r 16. They went to 16 inch from 15 inch due to the size of the front caliper. But, you can still fit 15 in. wheels with 215/70 r -15 You need an adapter, 1.25 inch will do, and you will have to grind about 1/32 of an inch off the top of the caliper body. This will not affect the caliper. Check out (rigged.up ) or Ford wheel spacers. Rear calipers are standard size.
According to the 1998 Mercury Grand Marquis Owner Guide : ( 71.9 litres / 19.0 U.S. gallons )
The 1998 Mercury Grand marquis has the 4.6 liter / 281 cubic inch Single Over Head Cam ( SOHC ) engine from the factory
Here they are: Driver = 22"Passenger = 22"
A 1998 Mercury Grand Marquis came from the factory with the 4.6 liter ( 281 cubic inch ) Single Over Head Cam , V8 engine
Should be 16 inch. Although some might have 15 inch, but that depends on the size of the front calipers. If the calipers are the new larger type, then 16 inch wheels.
The Mercury Grand Marquis is a nice big car, especially those from 1986, very roomy for those who are tall, with long legs. The original tires size for this vehicle is 215/70-15. There is no other size suggestions for this vehicle.
According to the 1998 Mercury Grand Marquis Owner Guide ( and one of Fords websites ) The ( Motorcraft FL-820-S ) engine oil filter is used
6x8
15 inch
Which ones?
4x6
20 gallons