Isuzu Cars and Trucks 1981-1991

Fuel Recommendations



The engine is designed to operate on unleaded gasoline ONLY and is essential for the proper operation of the emission control system. The use of unleaded fuel will reduce spark plug fouling, exhaust system corrosion and engine oil deterioration.

In most parts of the United States, fuel with an octane rating of 87 should be used; in high altitude areas, fuel with an octane rating as low as 85 may be used. However, the high performance engines are recommended to use a fuel with an octane rating of 93 or greater. Using fuels with a lower octane may decrease engine performance, increase emissions and engine wear.

In some areas, fuel consisting of a blend of alcohol may be used; this blend of gasoline and alcohol is known as gasohol. When using gasohol, never use blends exceeding 10% ethanol or 5% methanol.

The use of fuel with excessive amounts of alcohol may jeopardize the new car warranties.


Fuel manufacturers produce two grades of diesel fuel, No. 1 and No. 2, for use in automotive diesel engines. Generally speaking, No. 2 fuel is recommended over No. 1 for driving in temperatures above 20and#x00B0;F (-7and#x00B0;C). In fact, in many areas, No. 2 diesel is the only fuel available. By comparison, No. 2 diesel fuel is less volatile than No. 1 fuel, and gives better fuel economy. No. 2 fuel is also a better injection pump lubricant.

Two important characteristics of diesel fuel are its cetane number and its viscosity.

The cetane number of a diesel fuel refers to the ease with which a diesel fuel ignites. High cetane numbers mean that the fuel will ignite with relative ease so that it ignites well in an engine being cranked at low temperatures. Naturally, the lower the cetane number, the higher the temperature must be to ignite the fuel. Most commercial fuels have cetane numbers that range from 35 to 65. No. 1 diesel fuel generally has a higher cetane rating than No. 2 fuel.

Viscosity is the ability of a liquid, in this case diesel fuel, to flow. Using straight No. 2 diesel fuel below 20and#x00B0;F (-7and#x00B0;C) can cause problems, because this fuel tends to become cloudy, meaning wax crystals begin forming in the fuel. 20and#x00B0;F (-7and#x00B0;C) is often called the cloud point for No. 2 fuel. In extreme cold weather, No. 2 fuel can stop flowing altogether. In either case, fuel flow is restricted, which can result in a no start condition or poor engine performance. Fuel manufacturers often winterize No. 2 diesel fuel by using various fuel additives and blends (No. 1 diesel fuel, kerosene, etc.) to lower its winter time viscosity. Generally speaking, though, No. 1 diesel fuel is more satisfactory in extremely cold weather.

No. 1 and No. 2 diesel fuels will mix and burn with no ill effects, although the engine manufacturer will undoubtedly recommend one or the other. Consult the owner's manual for information.

Depending on local climate, most fuel manufacturers make winterized No. 2 fuel available seasonally.

Many automobile manufacturers (Oldsmobile, for example) publish pamphlets giving the locations of diesel fuel stations nationwide. Contact the local dealer for information.

Do not substitute home heating oil for automotive diesel fuel. While basic characteristics of these oils are similar, the heating oil is not capable of meeting diesel cetane ratings. This means that using it might offer not only hard starting but engine knock; even under warm operating conditions. This could result in unnecessary engine wear or damage.

Further, furnace oil is not blended for operation at colder temperatures as most heating oil filters are located indoors. It could easily clog fuel filters with wax.

The equipment used in burning furnace oil does not contain the extremely fine machined surfaces or extremely tiny nozzle openings used in a diesel engine fuel system. Very small amounts of dirt and abrasives that will pass right through a heating oil fuel system could play havoc with your diesel's injection system. Finally, minimum standards regarding sulfur and ash that help keep deposits out of your diesel engine and minimize corrosion may not be met by furnace oil.

One more word on diesel fuels. Don't thin diesel fuel with gasoline. The result is the most highly explosive mixture possible in your fuel tank and unwarranted danger. Fuel thinned with gasoline may not adequately lubricate the injection system, leading to premature pump and nozzle failure and need for an expensive overhaul. Cetane rating will also be effected in an undesirable way.

It's best to buy No. 1 or blended No. 2 fuel for wintertime use. If you must use some means to keep No. 2 fuel from waxing, blend it with No. 1 or use a quality anti-waxing agent.