All Chevrolet Novas and Geo Prizms use unleaded fuel of 91 research octane (RON) or higher. Regular leaded fuel may not be used in these models because they are equipped with a catalytic converter for emission control purposes. Leaded fuel will render the converter useless, raising the emission content of the exhaust to illegal and environmentally unacceptable levels. It will also block the converter passages, increasing exhaust back pressure; in extreme cases, exhaust blockage will be raised to the point where the engine will not run.
Fuels of the same octane rating have varying anti-knock qualities. Thus if your engine knocks or pings, try switching brands of gasoline before trying a more expensive higher octane fuel.
Your engine's fuel requirements can change with time, due to carbon buildup which changes the compression ratio. If switching brands or grades of gas doesn't work, check the ignition timing.
See Figure 1
The SAE (Society of Automotive Engineers) 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.
Oil viscosities should be chosen from the oils recommended for the lowest anticipated temperatures during the oil change interval. Multi-viscosity oils (5W-30, 10W-30 etc..) offer the important advantage of being adaptable to temperature extremes. They allow easy starting at low temperatures, yet they give good protection at high speeds and engine temperatures. This is a decided advantage in changeable climates or in long distance touring. For recommended oil viscosities, refer to the engine oil viscosity chart.
The API (American Petroleum Institute) designation indicates the classification of engine oil for use under given operating conditions. Only oils designated for Service SG/SC, SG/CD or just SG, should be used. These oils provide maximum engine protection. Both the SAE grade number and the API designation can be found on the top of a can of oil.
Non-detergent or straight mineral oils should not be used. Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval.