According to one of Fords websites :
For a 2004 Ford Explorer ( 4.0 liter V6 and 4.6 liter V8 engines )
The ( Motorcraft FL-820-S engine oil filter is used )
* also , the 4.0 takes ( 4.7 liters / 5.0 U.S. quarts of 5W-30 ) and the
4.6 L , V8 engine takes ( 5.7 liters / 6.0 quarts of 5W-20 )
( 5 quarts ) with engine oil filter change
The 2004 Ford Explorer owners manual shows , for the 4.0 L SOHC - V6 engine : ( Motorcraft FL - 820S ) oil filter
On the 1997 Ford Explorer XLT : for the 4.0 L SOHC engine - Motorcraft FL-1A oil filter for the 5.0 L V8 engine - Motorcraft FL-820S oil filter according to the owners manual
5 quarts WITH FILTER CHANGE
7 quarts when changing the filter
V6 L14459 or PH9688
Mopar 5281090
Your 1991 Ford Explorer 4.0 liter takes 5 quarts ( 4.7 liters ) of motor oil WITH FILTER CHANGE
For the 4.0 liter V6 engine ( 5W-30 ) For the 4.6 liter V8 engine ( 5W-20 ) According to the 2004 Ford Explorer Owner Guide
from 2004 and newer they do not have oil filters, your 2006 does not use an oil filtrer.
Hp 2004
pf47