However, generally speaking, a 2000 Mustang likely requires one of the following:
* 5W-20: This is a common weight for many engines in that era.
* 5W-30: This is also possible, depending on the climate and engine specifics.
Crucially: The owner's manual will also specify if the engine requires synthetic, synthetic blend, or conventional oil. Using the incorrect type or weight of oil can damage your engine.
In short: Do not guess. Consult your owner's manual or the under-hood sticker for the definitive answer.