It came from the factory with ( 5W-30 )
Try above oil filter
The recommended oil is SAE 5W-20
According to the 1999 Ford Mustang Owner Guide : With engine oil filter change ( 5.0 quarts / 4.7 liters of engine oil )
The Ford recommended oil weight is 5w-20
1964 1/2 Shleby mustang 1965 Mustang GT 1966 Mustang GT 1967 Mustang GT 1968 Mustang GT/CS 1969 Mustang Mach 1 1970 Mustang Mach 1 1971 Boss Mustang 1972 Mustang Mach 1 1973 Mustang Mach 1 1979 Mustang 1982 Mustang GT 1983 Mustang GT 1984 Mustang GT 1985 Mustang GT 1986 Mustang GT 1987 Mustang GT 1988 Mustang GT 1989 Mustang LX 1990 Mustang GT 1991 Mustang GT 1992 Mustang GT convertible 1993 Mustang GT/Saleen(possible) 1993 Mustang Cobra 1994 Mustang Cobra/GT 1995 Mustang GT 1996 Mustang Cobra 1997 Mustang Cobra 1999 Mustang Cobra 2001 Mustang GT/Cobra 2002 Saleen Mustang S-281-E/Mustang GT 2003 Mustang Cobra 2004 Mustang GT 2005 Mustang GT 2006 Mustang GT 2007 Mustang GT 2008 Mustang GT P.S. Shelby used to be the original mustang owner in the 1960s but in later years was bought out by Ford -Doug
My 2003 mustang gt sump is 6 quarts
2810 lbs
# 168 according to the 1999 Ford Mustang owners manual
6 QT
about 8000
Cable.