Chrysler Full-Size Trucks 1997-2000 Repair Guide

Fuel and Engine Oil Recommendations


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


All late model trucks are designed to run on unleaded gasoline. Any vehicle originally equipped with a catalytic converter MUST use unleaded gasoline.

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Fig. Gasoline engine oil viscosity chart

The recommended oil viscosities for sustained temperatures ranging from below -10ºF (-23ºC) to above 100ºF (38ºC) are listed in this section. They are broken down into multi-viscosities and single viscosities. Multi-viscosity oils are recommended because of their wider range of acceptable temperatures and driving conditions.

When adding oil to the crankcase or when changing the oil and filter, it is important that oil of an equal quality to original equipment be used in your truck. The use of inferior oils may void the warranty, damage your engine, or both.

The Society of Automotive Engineers (SAE) grade number indicates the oil's viscosity (its ability to lubricate at a given temperature). The lower the SAE number, the lighter the oil; the lower the viscosity, the easier it is to crank the engine in cold weather but the less the oil will lubricate and protect the engine in high temperatures. This number is marked on every oil container.

Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval. Due to the need for an oil that embodies both good lubrication at high temperatures and easy cranking in cold weather, multigrade oils have been developed. Basically, multigrade oil is thinner at low temperatures and thicker at high temperatures. For example, a 10W-40 oil exhibits the characteristics of a 10 weight (SAE 10) oil when the truck is first started and the oil is cold. Its lighter weight allows it to travel to the lubricating surfaces quicker and offer less resistance to starter motor cranking than, say, a straight 30 weight (SAE 30) oil. But after the engine reaches operating temperature, the 10W-40 oil has about the same viscosity that straight 40 weight (SAE 40) oil would have at that temperature.

The American Petroleum Institute (API) designations, also found on the oil container, indicate the classification of engine oil used under certain given operating conditions. Only oils designated for use Service SJ (or a later superceding designation) heavy-duty detergent should be used in your truck. Oils of the SJ type perform may functions inside the engine besides their basic lubrication. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents high and low temperature deposits, while keeping sludge and dirt particles in suspension. The oil neutralizes acids, particularly sulfuric acid, as well as other by products of engine combustion. If these acids are allowed to concentrate, they can cause corrosion and rapid wear of the internal engine parts.

Non-detergent motor oils or straight mineral oils should NOT be used in your gasoline engine.


Diesel engines require different engine oil from those used in gasoline engines. Besides providing the protection that gasoline engine oil does, diesel oil must also deal with increased engine heat and the diesel blow-by gases, which create sulfuric acid, a highly corrosive substance.

Under the American Petroleum Institute (API) classifications, gasoline engine oil codes begin with an S , and diesel engine oil codes begin with a C . This first letter designation is followed by a second letter code, which explains what type of service (heavy, moderate, light) the oil is meant for. For example, the label of a typical oil bottle may well include: API SERVICES SF, CD. This means the oil is superior, heavy-duty engine oil and can be used in a diesel engine.

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Fig. Diesel engine viscosity chart

Many diesel manufacturers recommend oil that has both gasoline and diesel engine API classifications.

The manufacturer specifies the use of engine oil that conforms to API quality "CE," or "CE/SG." Oils with high ash content are not recommended as they may cause deposits on the valves. A maximum of 1.85 % sulfated ash content is recommended for the diesel engines covered in this guide.

Fuel makers commonly produce two grades of diesel fuel for use in automotive diesel engines No. 1 and No. 2. Generally speaking, No. 2 fuel is recommended over No. 1 for driving in temperatures above 20ºF (7ºC). 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. Also, No. 2 fuel is a better injection pump lubricant.

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 or that it ignites well 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 35-65. No. 1 diesel fuel generally has a higher cetane rating than No. 2 fuel.

As the temperature goes down, diesel fuel tends to thicken. Diesel fuel contains paraffins (wax) and at low ambient temperatures, wax crystals begin forming in the fuel. The temperature at which this occurs is known as the cloud point. The cloud point for diesel fuel varies due to its composition and that information should be available from your fuel supplier or gas station. A typical cloud point temperature is 10ºF (-12ºC). This is an important piece of information since, in extremely cold weather, diesel fuel can stop flowing altogether. This can result in no start condition or poor engine performance.

Depending on local climate, most fuel manufacturers make winterized No. 2 fuel available seasonally. The manufacturers often winterize No. 2 diesel fuel using various fuel additives and blends (No. 1 diesel fuel, kerosene, etc.) to lower its wintertime 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.

Many automobile manufacturers publish pamphlets giving the locations of diesel fuel stations nationwide. Contact a local dealer for information.

When planning a trip with a diesel powered vehicle, take into account the temperature of your destination. While your local temperature may be high enough for good running, lower temperatures at the destination may cause clouding and plugging.

Do NOT substitute home heating oil for automotive diesel fuel. While in some cases, home heating oil refinement levels equal those of diesel fuel, many times they are far below diesel engine requirements. The result of using dirty home heating oil will be a clogged fuel system, in which case the entire system may have to be dismantled and cleaned.

One more word on diesel fuels. Don't thin diesel fuel with gasoline in cold weather. The lighter gasoline, which is more explosive, will cause rough running at the very least, and may cause extensive damage to the fuel system if enough is used.