GM Century/Lumina/Grand Prix/Intrigue 1997-2000

Fuel and Engine Oil Recommendations



Some fuel additives contain chemicals that can damage the catalytic converter and/or the oxygen sensors. Read all of the labels carefully before using any additive in the engine or fuel system. The owner's manual should also be consulted.

All of the vehicles covered by this guide are designed to run on unleaded fuel. The use of a leaded fuel in a vehicle requiring unleaded will plug the catalytic converter and render it inoperative. It will also increase exhaust backpressure because the material in the converter will tend to collapse and plug the exhaust, severely reducing engine power. 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 octane ratings. Fuel should be selected for the brand and octane which performs best with your engine.

All of the engines covered by this guide require a fuel with an octane rating of 87 or higher, except for the 3.8L (VIN 1) supercharged engine which requires premium fuel with an octane rating of 92 or higher.

The use of a fuel too low in octane (a measure of anti-knock quality) will result in spark knock. While the computer controlled ignition system uses knock sensors to detect knock and then electronically adjust the ignition timing to compensate, there is a limit to the system's adjustment capability. Since many factors such as altitude, terrain, air temperature and humidity affect operating efficiency, some light knocking (usually on acceleration) may result and is even considered normal. But 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.


The Society of Automotive Engineers (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, and the easier it should be 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. The information found in your owner's manual will give you the best recommendations for your vehicle.

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 driving.

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Fig. Look for the API oil identification label when choosing your engine oil

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Fig. Recommended SAE engine oil viscosity grades for gasoline engines

The American Petroleum Institute (API) designation indicates the classification of engine oil used under certain given operating conditions. Only oil designated for Service SJ, or the latest superseding oil grade should be used. Oils of the SJ type perform a variety of functions inside the engine in addition to their basic function as a lubricant. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents the formation of high and low temperature deposits and also keeps sludge and particles in suspension. Acids, particularly sulfuric acid, one of several by-product of the combustion process, are neutralized by the additive package in the oil. Both the SAE grade number and the API designation can be found on the side of the oil bottle.

Synthetic Oils

There are excellent synthetic and fuel-efficient oils available that, under the right circumstances, can help provide better fuel mileage and better engine protection. However, these advantages come at a price, which can be significantly more than the price per quart of conventional motor oils.

Before pouring any synthetic oils into your vehicle's engine, you should consider the condition of the engine and the type of driving you do. It is also wise to again, consult the owner's manual.

Generally, it is best to avoid the use of synthetic oil in both brand new and older, high mileage engines. New engine require a proper break-in, and some sources feel that the synthetics are so slippery, that they can impede the normal wear engines need for break in. Some manufacturers recommend that you accumulate at least 5,000 miles (8,000 km) before switching to a synthetic oil. Conversely, older engines are looser and tend to lose more oil; synthetics will slip past worn parts more readily than regular oil. If you engine already leaks oils (due to worn parts or bad seals/gaskets), it may leak more with a synthetic oil.