According to fordparts.com
For a 1991 Ford Mustang :
Both the 2.3 liter four cylinder and the 5.0 liter V8 use the ( Motorcraft FL-1-A ) engine oil filter
On a 3.8L 95 mustang the oil filter mounts to the oil pump.
( Motorcraft FL-1-A ) engine oil filter for the 289 cubic inch V8 in a 1966 Ford Mustang
1998 FORD MUSTANG 3.8L 6-cyl Engine Code 4CAPACITIESEngine, with filter..........5.0 quartsWix Oil Filter...............515161998 FORD MUSTANG 4.6L 8-cyl Engine Code XCAPACITIESEngine, with filter..........5.0 quartsWix Oil Filter...............513721998 FORD MUSTANG 4.6L 8-cyl Engine Code V 32-valveCAPACITIESEngine, with filter..........6.0 quartsWix Oil Filter...............51372Hope This Helps.
Motorcraft ( FL-400-S ) engine oil filter for the 3.8 liter V6 in a 2001 Ford Mustang ( according to fordparts.com )
( 5 quarts ) with filter change - according to the 2000 Ford Mustang owners manual
The 2001 Ford Mustang owners manual shows ( 5 quarts ) of engine oil with filter change
The oil capacity is five with a new oil filter.
5 quarts with engine oil filter change ( for the 2.3 L and 5.0 L engines - according to my Chilton repair manual )
every 3,000 miles. oil and filter
My ( 1991 ) 5.0 LX Ford Mustang always used 5W-30 as recommended
My ( 1991 ) Ford Mustang 5.0 LX came from the factory with ( 5W-30 )
5 quarts ( 4.7 liters ) with engine oil filter change for your V6