Changing the oil in a GMC diesel is similar to changing the oil in a passenger car. The biggest difference is the diesel takes more oil and the oil filter is larger in size than a standard oil filter. The oil change intervals in a diesel are less frequent. Change the oil every 6,000 miles to prevent breakdown from the old motor oil. This should take only half an hour, as everything is easy to access.
Locate the oil pan underneath the motor. Place a drain pan underneath the oil pan.
Loosen the drain plug with a crescent wrench. Allow the oil to drain into your pan. Then re-tighten the drain plug.
Unscrew the oil filter sitting just ahead of the drain pan, using an oil filter wrench. Ensure you have your drain pan underneath the filter; some oil will drain out around the filter. Place the filter with the waste oil you collected. Dispose of these items properly.
Dab clean motor oil around the gasket of the new oil filter. This will make the filter easier to remove during the next oil change. This will also help to seal the gasket to the oil filter housing.
Pour 1 qt. of oil into the oil filter. This will help to prevent a dry start.
Screw the oil filter to the oil filter housing hand-tight. Do not wrench-tighten, as this would strip the threads on the filter.
Open the hood to access the engine compartment. Unscrew the oil filler cap on the crankcase. Pull the engine oil dipstick out of the tube. Wipe the dipstick clean with a fresh towel. Place it to the side.
Pour in 12 qts. of 15W-30 motor oil into the crankcase. Check the level by inserting the dipstick into the tube and pull back out. Check the level against the markings on the dipstick. Pour oil into the motor at 1/2 qt. intervals until the level indicates full.
Start the truck and allow it to run for five minutes. Turn the truck off and check the oil after five minutes of allowing the motor to cool.
