The year of your Mustang would be helpful. But is should be between 4-6 quarts depending on the engine.
Hope This Helps
Six quarts
With engine oil filter change ( 5 quarts / 4.7 liters of engine oil )
5 quarts ( 4.7 liters ) with engine oil filter change
I believe that takes 5 U.S. quarts with oil filter change
The 200 cubic inch straight 6 cylinder in a 1966 Ford Mustang holds ( 4 and 1/2 U.S. quarts with engine oil filter change )
I believe the 200 cubic inch straight 6 cylinder in a 1968 Ford Mustang takes (4.5 U.S. quarts ) with engine oil filter change
5.0Qts
According to the 2001 Ford Mustang Owner Guide : With engine oil filter change : The 3.8 liter V6 engine takes ( 4.7 liters / 5.0 U.S. quarts of 5W-20 )
3
I believe that is ( 5 ) U.S. quarts with engine oil filter change
2000 gallons.
12.5Qts