On your 1968 Ford F-100 your fuel filter is near the carburetor ( on top of the engine , below the engine air filter ) and is either a fuel filter that is installed in the rubber gas line or is an original type that is screwed into the carburetor
The oil capacity is five with a new oil filter.
Check your PCV valve.
I believe the 1993 Ford Explorer ( 4 door ) gas tank holds 19.3 U.S. gallons
I was looking in the 2006 Ford Focus owners manual and it shows that the air filter is a non - serviceable part . The air filter is designed to last the life of the vehicle . A Ford technician can check the diagnostic system to see if there is a possibility of an excessively dirty air filter
You can purchase this filter at a New Holland dealership. I could not locate an after-market replacement filter. Check link.
5 quarts with the filter, assuming you have the correct dip stick check it as you go...check it again after running as the filter does retain some oil.
If your 1976 Ford with 360 won't idle, check to ensure the air filter and fuel filter are free from debris. This can also indicate a problem with the carburetor.
I believe that is ( 4.5 quarts ) with engine oil filter change
check a car website
check fuel filter and pressure
Check air filter first and then change fuel filter. Fill the fuel filter with diesel before you change it ...