Chrysler Full-Size Trucks 1989-1996 Repair Guide

Fuel and Engine Oil Recommendations


See Figures 1 and 2

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Fig. Fig. 1: Look for the API oil identification label when choosing your engine oil

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Fig. Fig. 2: Before installing a new oil filter, coat the rubber gasket with clean oil


See Figures 3 and 4

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. Fig. 3: Gasoline engine oil viscosity chart

The recommended oil viscosities for sustained temperatures ranging from below -10°F (-23°C) to above 100°F (38°C) 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, a multigrade oil is thinner at low temperatures and thicker at high temperatures. For example, a 10W-40 oil (the W stands for winter) 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 begins acting like straight 40 weight (SAE 40) oil, its heavier weight providing greater lubrication with less chance of foaming than a straight 30 weight oil.

The American Petroleum Institute (API) designations, also found on the oil container, indicates the classification of engine oil used under certain given operating conditions. Only oils designated for use Service SF (or a later superceding designation) heavy duty detergent should be used in your truck. Oils of the SF 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. Acids, particularly sulfuric acid, as well as other by products of engine combustion, are neutralized by the oil. If these acids are allowed to concentrate, they can cause corrosion and rapid wear of the internal engine parts.

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Fig. Fig. 4: Standard markings found on engine oil containers that designate API service classifications, and other pertinent information


Non-detergent motor oils or straight mineral oils should not be used in your Plymouth/Dodge gasoline engine.


See Figure 5

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 a superior, heavy duty engine oil and can be used in a diesel engine.

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Fig. Fig. 5: Diesel engine viscosity chart

Many diesel manufacturers recommend an oil with both gasoline and diesel engine API classifications.

Chrysler Corp. specifies the use of an engine oil conforming to API service categories of BOTH SG and CD (or the latest superceding codes). DO NOT use oils labeled as only SG or only CD, as they could cause engine damage.

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 20°F (7°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. 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 35-3. 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 10°F (-12°C). This is an important piece of information as is 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 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.

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.