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 vehicles covered by this information are designed to run on unleaded fuel. The used 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.
For information regarding vehicles equipped with the Flexible Fuel (FF) system, refer to your owner's manual for fuel recommendations.
As far as the octane rating is concerned, refer to the General Engine Specifications Chart in Engine & Engine Overhaul to find your engine and its compression ratio. If the compression ration is 9.0:1 or lower, in most cases a regular unleaded grade of gasoline can be used. If the compression ratio is 9.0:1-9.3:1, use a premium grade of unleaded fuel.
The use of a fuel too low in octane (a measurement of antiknock 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 buildup, which will in turn change the compression ratio. If your 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 Figure 1
The SAE (Society of Automotive Engineers) 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.
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.
The API (American Petroleum Institute) designation indicates the classification of engine oil used under certain given operating conditions. Only oils designated for use Service SG, or the latest superceding oil grade, should be used. Oils of the SG 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 dirt particles in suspension. Acids, particularly sulfuric acid, as well as other byproducts of combustion, are neutralized. Both the SAE grade number and the API designation can be found of the side of the oil bottle. Oil meeting API classification SG, SG/CC or SG/CD is recommended for use in your vehicle. Ford has filled your crankcase with SAE 5W-30 and recommends that you continue to use this as long as the outside temperatures don't exceed 100°F (38°C). There are other options, however, such as SAE 10W-30; refer to the accompanying oil viscosity/ambient temperature chart.
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 three or four times the price per quart of conventional motor oils.
Before pouring any synthetic oils into your car's engine, you should consider the condition of the engine and the type of driving you do. It is also wise to check the vehicle manufacturer's position on synthetic oils.
Generally, it is best to avoid the use of synthetic oil in both brand new and older, high mileage engines. New engines require a proper break-in, and the synthetics are so slippery that they can impede this; most manufacturers recommend that you wait at least 5,000 miles (8,000 km) before switching to a synthetic oil. Conversely, older engines are looser and tend to use more oil; synthetics will slip past worn parts more readily than regular oil, and will be used up faster. If your car already leaks and/or uses oil (due to worn parts or bad seals/gaskets), it may leak and use more with a synthetic inside.
Consider your type of driving. If most of your accumulated mileage is on the highway at higher, steadier speed, a synthetic oil will reduce friction and probably help deliver better fuel mileage. If you choose to use synthetic oil in this case, synthetic oils which are certified and have the preferred viscosity may be used in your engine; however, the oil and filter must still be changed according to the maintenance schedule. Cars used under harder, stop-and-go, short hop circumstances should always be serviced more frequently, and for these cars, synthetic oil may not be a wise investment.