The 1991 Ford Explorer's oil fill location is typically on
top of the engine. It's usually a cap with a prominent marking indicating it's the oil fill. It's often marked with an oil can symbol. Look for a large cap near the center or towards the back of the engine.
However, it's always best to consult your owner's manual. A picture in the manual will definitively show you the location, and it will also specify the correct type and amount of oil for your vehicle.
