Isuzu Cars and Trucks 1981-1991

Oil Recommendations


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

The SAE (Society of Automotive Engineers) grade number of oil indicates the viscosity of the oil (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 at 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. Multigrade oils have been developed because of the need for an oil that embodies both good lubrication at high temperatures and easy cranking in cold weather. All oils are thick at low temperatures and thin out as the temperature rises. Basically, a multigrade oil is thinner at lower temperatures and thicker at high temperatures relative to straight weight oils. For example, a 10W40 oil (the W stands for winter) exhibits the characteristics of a 10 weight (SAE 10) oil when the vehicle 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 10W40 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 would at that temperature.

Single grade (straight weight) oils such as SAE 30 are more satisfactory than multi-viscosity oils for highway driving in diesel engines.


The API (American Petroleum Institute) designation, also found on the oil container, indicates the classification of engine oil used under certain given operating conditions. Only oils designated for use Service SE , or SF heavy duty detergent should be used in your vehicle. For 1984 and later models, only SF or SG oils are approved by Isuzu. Oils of the SE, SF and SG type perform many functions inside the engine besides their basic function of lubrication. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents high and low temperature deposits and also keeps 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.

Non-detergent or straight mineral oils should not be used in your GM engine.

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Fig. Gasoline engine oil viscosity chart


Diesel engines require different engine oil from those used in gasoline engines. Besides doing the things 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 compound.

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 top of a typical oil can will include: API SERVICES SC, SD, SE, CA, CB, CC . This means the oil in the can is a good, moderate duty engine oil when used in a diesel engine.

It should be noted here that the further down the alphabet the second letter of the API classification is, the greater the oil's protective qualities are (CD is the severest duty diesel engine oil, CA is the lightest duty oil, etc.) The same is true for gasoline engine oil classifications (SG is the severest duty gasoline engine oil, SA is the lightest duty oil, etc.).

Many diesel manufacturers recommend an oil with both gasoline and diesel engine API classifications. Consult the owner's manual for specifications.

The top of the oil can will also contain an SAE (Society of Automotive Engineers) designation, which gives the oil's viscosity. A typical designation will be: SAE 10W30, which means the oil is a winter viscosity oil, meaning it will flow and give protection at low temperatures.

On the diesel engine, oil viscosity is critical, because the diesel is much harder to start (due to its higher compression) than a gasoline engine. Obviously, if you fill the crankcase with a very heavy oil during the winter (SAE 20W50, for example) the starter is going to require a lot of current from the battery to turn the engine. And, since batteries don't function well in cold weather in the first place, you may find yourself stranded some morning. Consult the owner's manual for recommended oil specifications for the climate you live in.

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Fig. Diesel engine oil viscosity 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 vehicle's engine, you should consider the condition of the engine and the type of driving you do. Also, check the vehicle's warranty conditions regarding the use of synthetics.

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 prevent this; most manufacturers recommend that you wait at least 5,000 miles 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 vehicle already leaks and/or uses oil (due to worn parts and bad seals or gaskets), it will leak and use more with a slippery synthetic inside.

Consider your type of driving. If most of your accumulated mileage is on the highway at higher, steadier speeds, a synthetic oil will reduce friction and probably help delivery better fuel mileage. Under such ideal highway conditions, the oil change interval can be extended, as long as the oil filter will operate effectively for the extended life of the oil. If the filter can't do its job for this extended period, dirt and sludge will build up in your engine's crankcase, sump, oil pump and lines, no matter what type of oil is used. If using synthetic oil in this manner, you should continue to change the oil filter at the recommended intervals.

Vehicles used under harder, stop-and-go, short hop circumstances should always be serviced more frequently and for these vehicles synthetic oil may not be a wise investment. Because of the necessary shorter change interval needed for this type of driving, you cannot take advantage of the long recommended change interval of most synthetic oils.

Finally, most synthetic oils are not compatible with conventional oils and cannot be added to them. This means you should always carry a couple of quarts of synthetic oil with you while on a long trip, as not all service stations carry this oil.


Every time you stop for fuel, check the engine oil as follows:

  1. Make sure the car is parked on level ground.
  3. When checking the oil level it is best for the engine to be at normal operating temperature, although checking the oil immediately after stopping will lead to a false reading. Wait a few minutes after turning off the engine to allow the oil to drain back into the crankcase.
  5. Open the hood and locate the dipstick which will be on either the right or left side depending upon your particular engine. Pull the dipstick from its tube, wipe it clean and then reinsert it.
  7. Pull the dipstick out again and, holding it horizontally, read the oil level. The oil should be between the "FULL" and "ADD" marks, dots or in the checkered area on the dipstick. If the oil is below the bottom mark, add oil of the proper viscosity through the capped opening in the top of the cylinder head cover.
  9. Replace the dipstick and check the oil level again after adding any oil. Be careful not to overfill the crankcase. Approximately 1 quart of oil will raise the level from the upper mark to the "FULL" mark. Excess oil will generally be consumed at an accelerated rate.

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Fig. Oil level dipstick early model engines

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Fig. Oil level dipstick late model engines

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Fig. Oil level dipstick V6 engines


The oil is to be changed every 3,000 miles or the interval in your owner's manual. Under normal conditions, change the filter at first oil change and then at every other oil change, unless 6 months pass between changes. We recommend that the oil filter be changed every time the oil is changed. About a quart of dirty oil remains in the old filter. For a few dollars, it is a small expense for extended engine life.

  1. Allow the engine to reach normal operating temperature. Turn the engine OFF and allow to sit for about five minutes. Raise the car and support on jackstands. Remove the oil pan plug and drain oil into a catch pan.
  3. Using an oil filter wrench, remove the oil filter and place it in the oil catch pan. Using a clean rag, wipe oil filter mounting surface.

To install:

  1. When installing the oil filter, place a small amount of oil on the sealing gasket and tighten the filter only hand tight. Install the oil pan plug and torque to 20 ft. lbs. (27 Nm).
  3. Make sure the plug is tight in the pan. Using a funnel, add oil through the valve cover cap. Lower car, start the engine and inspect for oil leaks.

Run the engine at idle speed only until the oil pressure starts to rise. Engine damage may occur if the engine is raced with no oil pressure.

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Fig. By keeping inward pressure on the oil drain plug as you unscrew it, oil will not escape past the threads

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Fig. Remove the oil filter with a strap wrench

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Fig. Coat the new oil filter gasket with clean engine oil

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Fig. Install the new oil filter by hand. Be careful NOT to overtighten the oil filter

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Fig. Add oil through the capped opening in the cylinder head (valve) cover