FORD 2003 Explorer v.5 - Manual (Page 231)

4.0L Engine
Look for this certification
trademark.
Use SAE 5W-30 engine oil.
Only use oils “Certified For Gasoline Engines” by the American
Petroleum Institute (API). To protect your engine’s warranty use
Motorcraft SAE 5W-30 or an equivalent 5W-30 oil meeting Ford
specification WSS-M2C205–A.
Do not use supplemental engine oil additives, cleaners or other engine
treatments. They are unnecessary and could lead to engine damage that
is not covered by Ford warranty.
Change your engine oil according to the appropriate schedule listed in
the scheduled maintenance guide.
Ford production and aftermarket (Motorcraft) oil filters are designed for
added engine protection and long life. If a replacement oil filter is used
that does not meet Ford material and design specifications, start-up
engine noises or knock may be experienced.
It is recommended you use the appropriate Motorcraft oil filter (or
another brand meeting Ford specifications) for your engine application.
2003 Explorer (exp)
Owners Guide (post-2002-fmt)
USA English (fus)
Maintenance and Specifications
231