Some fuel additives contain chemicals that can damage the catalytic converter and/or oxygen sensor. Read all of the labels carefully before using any additive in the engine or fuel system.
All Neons are designed to run on unleaded fuel. The use of a leaded fuel in a car requiring unleaded fuel will plug the catalytic converter and render it inoperative. It will also increase exhaust backpressure to the point where engine output will be severely reduced. The minimum octane rating of the unleaded fuel being used must be at least 87, which usually means regular unleaded, but some high performance engines may require higher ratings. Fuel should be selected for the brand and octane which performs best with your engine. Judge a gasoline by its ability to prevent pinging, its engine starting capabilities (cold and hot) and general all weather performance.
As far as the octane rating is concerned, refer to the general engine specifications chart in Engine and Engine Rebuilding of this guide to find your engine and its compression ratio. If the compression ratio is 9.0:1 or lower, in most cases a regular unleaded grade of gasoline can be used. If the compression ratio is higher than 9.0:1 use a premium grade of unleaded fuel.
The use of a fuel too low in octane (a measure of anti-knock quality) will result in spark knock. Since many factors such as altitude, terrain, air temperature and humidity affect operating efficiency, knocking may result even though the recommended fuel is being used. If persistent knocking occurs, it may be necessary to switch to a higher grade of fuel. Continuous or heavy knocking may result in engine damage.
Your engine's fuel requirement can change with time, mainly due to carbon build-up, which will in turn change the compression ratio. If you engine pings, knocks or diesels (runs with the ignition OFF) switch to a higher grade of fuel. Sometimes, just changing brands will cure the problem. If it becomes necessary to retard the timing from the specifications, don't change it more than a few degrees. Retarded timing will reduce power output and fuel mileage, in addition to making the engine run hotter.
See Figures 1 and 2
The Society Of Automotive Engineer (SAE) grade number indicates the viscosity of the engine oil and thus its ability to lubricate at 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 those oils recommended for the lowest anticipated temperatures during the oil change interval. With the proper viscosity, you will be assured of easy cold starting and sufficient engine protection.