According to the 2003 Ford Thunderbird Owner Guide :
With engine oil filter change :
The 3.9 liter V8 engine takes ( 6.5 U.S. quarts of 5W-20 )
According to my Chilton's Auto Repair Manual : With engine oil filter change : The 1988 Ford Thunderbird engines ( 2.3 / 3.8 / 5.0 ) take : ( 5.0 U.S. quarts )
According to the ( 1996 ) Ford Thunderbird Owner Guide : With engine oil filter change : ( 5.3 U.S. quarts of 5W-30 , PREFERRED engine oil )
6 quarts
about 15qts
The 3.8 liter V6 engine in a 2003 Ford Mustang takes ( 5 quarts ) WITH ENGINE OIL FILTER CHANGE
WITH ENGINE OIL FILTER CHANGE : 4.5 quarts / 4.25 liters According to the 2003 Ford Escort owners manual
The 2003 Ford Excursion Owner Guide shows ( 6 quarts ) with engine oil filter change for the 5.4 liter V8 engine
( 6 quarts ) WITH ENGINE OIL FILTER CHANGE , according to the SVT supplement for the 2003 Ford F-150 lightning
6
( 4.5 quarts of engine oil ) with oil filter change for the 3.0 liter V6 ( according to the 2003 Ford Ranger Owner Guide )
The 2003 Ford Ranger owners manual shows : ( 4.5 quarts with filter change ) for the 3.0 L - V6 engine
Since you didn't tell us the Engine here are all three, Which Just happen to have the same Transmission. 1992 FORD THUNDERBIRD 3.8L 6-cyl Engine Code 41992 FORD THUNDERBIRD 3.8L 6-cyl Engine Code R1992 FORD THUNDERBIRD 5.0L 8-cyl Engine Code T HO CAPACITIESAutomatic Transmission, Initial Fill..........3.0 quarts[2]Automatic Transmission, Total Fill..........12.0 quarts [2] With ENG at operating temperature, shift through all gears. Check fluid level in PARK and add fluid as needed.