GM Full Size Vans 1967-1986 Repair Guide




See Figures 1 and 2

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Fig. Fig. 1: Gasoline engine recommended oil viscosities

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Fig. Fig. 2: Recommended diesel engine oil viscosities

The SAE grade number indicates the viscosity of the engine oil, or its ability to lubricate under 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.

The API (American Petroleum Institute) designation indicates the classification of engine oil for use under given operating conditions. Only oils designated for "Service SF'' should be used. These oils provide maximum engine protection. Both the SAE grade number and the API designation can be found on the top of a can of oil.

Non-detergent should not be used.

Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval.

The multi-viscosity oils offer the important advantage of being adaptable to temperature extremes. They allow easy starting at low temperatures, yet give good protection at high speeds and engine temperatures. This is a decided advantage in changeable climates or in long distance driving.

Diesel engines also require SF engine oil. In addition, the oil must qualify for a CC rating. The API has a number of different diesel engine ratings, including CB, CC, and CD.

1981 and later diesel engines can use either SF/CC or SF/CD rated oils.

The diesel engines in the Chevrolet and GMC trucks require SF/CC rated oil. DO NOT use an oil if the designation CD appears anywhere on the oil can. Use SF/CC engine oil only. Do not use an oil labeled only SF or only CC. Both designations must appear.

For recommended oil viscosities, refer to the chart. 10W-30 grade oils are not recommended for sustained high speed driving.

Single viscosity oil (SAE 30) is recommended for sustained high speed driving.


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. Also, check the truck'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 5000 miles (8045 km) before switching to a synthetic oil. Conversely, older engines are looser and tend to use more oil. Synthetics will slip past worn pats more readily than regular oil, and will be used up faster. If your car 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 deliver 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.

Trucks 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. 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.


See Figures 3, 4 and 5

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Fig. Fig. 3: Remove the engine oil dipstick and check the oil level

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Fig. Fig. 4: If necessary, remove the oil filler cap ...

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Fig. Fig. 5: ... and add the proper amount and grade of oil

The engine oil should be checked on a regular basis, ideally at each fuel stop. If the van is used for trailer towing or for heavy duty use, it would be safer to check it more often.

When checking the oil level it is best that the oil be at operating temperature, although checking the level immediately after stopping will give a false reading because all of the oil will not yet have drained back into the crankcase. Be sure that the van is resting on a level surface, allowing time for the oil to drain back into the crankcase.

  1. Open the hood or engine compartment and locate the dipstick. Remove it from the tube. The oil dipstick is located on the passenger's side of 6 cylinder engines and on the driver's side of V8s.
  3. Wipe the dipstick with a clean rag.
  5. Insert the dipstick fully into the tube, and remove it again. Hold the dipstick horizontally and read the oil level. The level should be between the "FULL'' and "ADD OIL'' marks. If the oil level is at or below the "ADD OIL'' mark, oil should be added as necessary. Oil is added through the capped opening on the valve cover(s). See Oil and Fuel Recommendations for proper viscosity and oil to use.
  7. Replace the dipstick and check the level after adding oil. Be careful not to overfill the crankcase. There is about 1 quart between the marks.


See Figures 6 and 7

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Fig. Fig. 6: Look for the API oil identification label when choosing your engine oil

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Fig. Fig. 7: Before installing a new oil filter, lightly coat the rubber gasket with clean oil

Engine oil should be changed according to the schedule in the Maintenance Interval Chart. Under conditions such as:

Driving in dusty conditions
Continuous trailer pulling or RV use
Extensive or prolonged idling
Extensive short trip operation in freezing temperatures (when the engine is not thoroughly warmed up)
Frequent long runs at high speeds and high ambient temperatures
Stop-and-go service such as delivery trucks

the oil change interval and filter replacement interval should be cut in half. Operation of the engine in severe conditions such as a dust storm may require an immediate oil and filter change.

Chevrolet and GMC recommended changing both the oil and filter during the first oil change and the filter every other oil change thereafter. For the small price of an oil filter, it's cheap insurance to replace the filter at every oil change. One of the larger filter manufacturers points out in its advertisements that not changing the filter leaves one quart of dirty oil in the engine. This claim is true and should be kept in mind when changing your oil.

The oil filter on the diesel engines must be changed every oil change.

To change the oil, the truck should be on a level surface, and the engine should be at operating temperature. This is to ensure that the foreign matter will be drained away along with the oil, and not left in the engine to form sludge. You should have available a container that will hold a minimum of 8 quarts of liquid, a wrench to fit the old drain plug, a spout for pouring in new oil, and a rag or two, which you will always need. If the filter is being replaced, you will also need a band wrench or filter wrench to fit the end of the filter.

If the engine is equipped with an oil cooler, this will also have to be drained, using the drain plug. Be sure to add enough oil to fill the cooler in addition to the engine.

  1. Position the truck on a level surface and set the parking brake or block the wheels. Slide a drain pan under the oil drain plug.
  3. From under the truck, loosen, but do not remove the oil drain plug. Cover your hand with a rag or glove and slowly unscrew the drain plug.

The engine oil will be HOT. Keep your arms, face and hands clear of the oil as it drains out.

  1. Remove the plug and let the oil drain into the pan.

Do not drop the plug into the drain pan.

  1. When all of the oil has drained, clean off the drain plug and put it back into the hole. Remember to tighten the plug 20 ft. lbs. (27 Nm) on gasoline engines or 30 ft. lbs. (40 Nm) for diesel engines.
  3. Loosen the filter with a band wrench or special oil filter cap wrench. On most Chevrolet engines, especially the V8s, the oil filter is next to the exhaust pipes. Stay clear of these, since even a passing contact will result in a painful burn.

On trucks equipped with catalytic converters stay clear of the converter. The outside temperature of a hot catalytic converter can approach 1,200°F (648°C).

  1. Cover your hand with a rag, and spin the filter off by hand.
  3. Coat the rubber gasket on a new filter with a light film of clean engine oil. Screw the filter onto the mounting stud and tighten according to the directions on the filter (usually hand tight one turn past the point where the gasket contacts the mounting base). Don't overtighten the filter.
  5. Refill the engine with the specified amount of clean engine oil.
  7. Run the engine for several minutes, checking for leaks. Check the level of the oil and add oil if necessary.

When you have finished this job, you will notice that you now possess four or five quarts of dirty oil. The best thing to do with it is to pour it into plastic jugs, such as milk or antifreeze containers. Then, if you are on good terms with you gas station man, he might let you pour it into his used oil container for recycling. Otherwise, the only thing to do with it is to put the containers into the trash.