* Check your owner's manual: This is the most important step. It will specify the recommended viscosity (e.g., 5W-30, 10W-30) and oil type (conventional, synthetic blend, or full synthetic).
* If you don't have the manual: For both engines, a 5W-30 is a very common and generally suitable viscosity, especially for a vehicle of that age. However, your climate might influence this slightly – a 10W-30 might be better in very hot climates.
* Oil Type: While conventional oil is perfectly acceptable and often less expensive, synthetic blend or full synthetic oils offer better protection and longer life, particularly if the Jeep is frequently used in harsh conditions (off-roading, extreme temperatures).
In short: Find your owner's manual. If you can't find it, a 5W-30 (conventional, synthetic blend, or full synthetic) is a safe bet, but always double-check before purchasing. The type of oil (conventional, synthetic blend, or full synthetic) is a matter of preference and budget.
