GM Full-Size Trucks 1970-1979 Repair Guide

Engine

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OIL LEVEL CHECK



See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: Check the crankcase oil level with the dipstick



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Fig. Fig. 2: Wipe dipstick using a clean, lint free cloth, then reinsert it in order to get the correct level



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Fig. Fig. 3: Withdraw the stick again and read the level while holding it horizontally - the oil should appear between the ADD and FULL marks on the dipstick



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Fig. Fig. 4: Remove the engine oil fill cap from the valve cover or filler tube (as applicable) ...



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Fig. Fig. 5: ... then add the correct type and amount of engine oil using a funnel to prevent a mess

The engine oil should be checked on a regular basis, ideally at each fuel stop. If the truck 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 truck is resting on a level surface, allowing time for the oil to drain back into the crankcase.

  1. Open the hood 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.
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  3. Wipe the dipstick with a clean rag.
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  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) on gasoline engines. Diesel engines have a capped oil fill tube at the front of the engine. See Oil and Fuel Recommendations for the proper viscosity oil to use.
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  7. Replace the dipstick and check the level after adding oil. Be careful not to overfill the crankcase. Approximately one quart of oil will raise the level from ADD to FULL.
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OIL AND FILTER CHANGE



See Figures 6, 7, 8, 9 and 10



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Fig. Fig. 6: The oil drain plug is located at the lowest point of the engine oil pan - if you don't have the proper size wrench or socket, an adjustable can be used to carefully carefully loosen it



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Fig. Fig. 7: The best way to loosen the drain plus is to use the proper sized wrench (or socket) ...



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Fig. Fig. 8: ... then quickly withdraw the plug and allow the oil to completely drain into a suitable pan



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Fig. Fig. 9: Use a strap wrench to loosen the oil filter; install the new filter by hand



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Fig. Fig. 10: 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 bank 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.
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  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.
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CAUTION
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.
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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) for gasoline engines or to 30 ft. lbs. (41 Nm) for diesel engines.
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  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.
  4.  


CAUTION
On trucks equipped with catalytic converters stay clear of the converter. The outside temperature of a hot catalytic converter can approach 1200 degrees F.

  1. Cover your hand with a rag, and spin the filter off by hand.
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  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.
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  5. Refill the engine with the specified amount of clean engine oil.
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  7. Run the engine for several minutes, checking the leaks. Check the level of the oil and add oil if necessary.
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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 your 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.

 
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