According to the Owner Guide :
For the 2.0 liter 4 cylinder engine ( Motorcraft FL-2005 )
For the 2.5 liter V6 engine ( Motorcraft FL-820 )
near the oil filter
For a Mercury Cougar , 2.5 litre V6 engine : According to the 1999 to 2002 Owner Guides : ( Motorcraft FL-820 engine oil filter )
Gasket should be included with new oil filter
If it is a V6 about 6 Quarts with a new oil filter.
I pretty sure your looking at 5 with the filter.
According to one of Fords websites : For the 1972 Mercury Cougar , 5.8 liter / 351 cubic inch V8 engine : ( Motorcraft FL-1-A engine oil filter )
Using a 1969 Ford Mustang or a 1969 Mercury Cougar with the 351 cubic inch / 5.8 litre V8 as examples : ( Motorcraft FL-1-A engine oil filter )
According to my Chilton's Auto Repair Manual : For the 3.8 liter V6 engine in a 1991 Mercury Cougar : With engine oil filter change : ( 5.0 US. quarts )
where it located the fill fiter on 1979 rx7cougar
According to the 2000 Mercury Cougar Owner Guide : With engine oil filter change : The 2.5 liter V6 engine takes ( 5.5 liters of 5W-30 engine oil )
According to the 2001 Mercury Cougar Owner Guide : For the 2.0 litre four cylinder engine : ( with engine oil filter change , 4.25 litres / 4.5 U.S. quarts of 5W-20 engine oil )
On a 1991 Mercury Cougar : The oil pump is INSIDE the oil pan ( the oil pan is bolted to the bottom of the engine )