All models through 1974 were originally designed to use a regular grade of gasoline. All 1975 and later models must use unleaded gasoline.
See Figures 1 and 2
Many factors help to determine the proper oil for your Jeep. The big question is what viscosity to use and when. The whole question of viscosity revolves around the lowest anticipated ambient temperature to be encountered before your next oil change. The recommended viscosity ratings for temperatures ranging from below 0°F (-18°C) to above +32°F (0°C) are listed in the accompanying chart. They are broken down into multi-viscosities and single viscosities. Multi-viscosity oils are recommended because of their wider range of acceptable temperatures and driving conditions.
The SAE grade number indicates the viscosity of the engine oil, or its ability to lubricate under a given temperature. The lower the SAE grade number, the lighter the oil. The lower the viscosity, the easier it is to crank the engine in cold weather.
The API (American Petroleum Institute) designation indicates the classification of engine oil for use under given operating conditions. For gasoline engines, only oils designated for Service SF/SG, or just SF, should be used. You can find the SF or SG marking either on the top or on the side of the container. The viscosity rating should be in the same place. Select the viscosity rating to be used by your type of driving and the temperature range anticipated before the next oil change.
The multi-viscosity oils offer the advantage of being adaptable to temperature extremes. They allow easy starts at low temperatures, yet still give good protection at high speeds and warm temperatures.