Ford 1999 Windstar Owner's Manual page 194

Maintenance and care
Engine oil and filter recommendations
Look for this certification mark.
Ford oil specification is WSS-M2C153-G.
Use SAE 5W-30 motor oil certified for gasoline engines by the American
Petroleum Institute.
Do not use supplemental engine oil additives, oil treatments or engine
treatments. They are unnecessary and could, under certain conditions,
lead to engine damage which is not covered by your warranty.
Change your engine oil and filter 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, startup
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.
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