Once you know the engine size, consult your owner's manual for the recommended oil viscosity and type (conventional, synthetic blend, or full synthetic). The manual will specify the weight, such as 5W-30 or 10W-30. It may also specify API certifications (like SN or SM). Using the incorrect viscosity can lead to engine damage.
Generally speaking, for a 1999 vehicle, a conventional oil meeting the manufacturer's specifications is perfectly acceptable. However, synthetic blend or full synthetic oils offer better protection and longer drain intervals. Always adhere to the specifications found in your owner's manual for the best results. Ignoring this advice could lead to costly engine repairs.
