* SAE 5W-30: This is a common recommendation for many 1999 Ranger engines and is suitable for a wide range of temperatures. It's a good all-around choice.
* SAE 10W-30: This is another possibility, particularly in warmer climates.
* Oil type: The owner's manual will also specify if it requires conventional, synthetic blend, or full synthetic oil. Conventional oil is typically the most affordable, while synthetic offers better performance and longevity.
To find the exact recommendation, you MUST consult your owner's manual. The manual will detail the specific oil viscosity (like 5W-30 or 10W-30) and type (conventional, synthetic blend, or full synthetic) recommended for your particular Ranger's engine. Ignoring this could damage your engine.