The recommended oil weight for a Mustang 5.0 depends on the year and specific engine. There's no single answer. You must consult your owner's manual.
The owner's manual will specify the recommended weight and type of oil (e.g., 5W-30, 5W-20, 10W-30) for your particular vehicle's engine and operating conditions (climate, etc.). Using the wrong weight oil can damage your engine.
