Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2024 and earlier GM passenger cars and gasoline-powered light duty trucks under 8500 lb GVW.

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  Models: 2024 and Prior GM Passenger Cars and Gasoline-Powered Light Duty Trucks Under 8500 LB GVW

Possible causes

• Towing a trailer increases oil consumption, which may then not meet the normal accepted rate given for an unloaded vehicle in personal use.

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  Towing a trailer will increase oil consumption and may cause oil consumption to fall below the normal accepted rate referenced in this bulletin for an unloaded vehicle in a personal use application.

• On vehicles usually driven short distances, especially in colder weather, unburned fuel and condensation may not evaporate out of the oil, and the dipstick may then show an over-full level.

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  On vehicles that are usually driven short distances, less than 8 km (5 mi), especially in colder weather, unburned fuel and condensation generated from cold engine operation may not get hot enough to evaporate out of the oil. When this occurs, the dipstick may indicate that the oil level is over-full.

• Piston scuffing, excessive piston-to-wall clearance, tapered or out of round cylinders, and worn, damaged or improperly installed valve guides, seals and piston rings all increase oil consumption.

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  Piston scuffing, excessive piston-to-wall clearance, tapered or out of round cylinders, worn, damaged or improperly installed valve guides, seals and piston rings will all cause an increase in oil consumption.

Steps to confirm (in the document’s order)

1. Inspect the oil pan and engine covers for leakage from over-tightened, damaged or out of place gaskets, and the oil lines and fittings for signs of leakage.

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   Inspect the oil pan and engine covers for leakage due to over-tightened, damaged, or out of place gaskets. Inspect oil lines and fittings for signs of leakage.

2. Verify that the dipstick tube is fully seated in the block.

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   Verify that the dipstick tube is fully seated in the block.

3. Let the vehicle sit for at least 15 minutes after the engine is shut off before reading the oil level.

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   To assure a sufficient amount of oil has drained back to the crankcase, and an accurate reading can be obtained, the vehicle should be allowed to sit for at least 15 minutes, after the engine has been shut off, before taking an oil level reading.

4. Verify that the PCV system operates properly; blockages, restrictions or damage in it can increase oil use.

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   Verify that the positive crankcase ventilation (PCV) system is operating properly. Blockages, restrictions, or damage to the PCV system can result in increased oil use.

5. Do not test oil economy until the vehicle has accumulated at least 6400 km (4000 mi).

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   Therefore, oil economy should not be tested until the vehicle has accumulated at least 6400 km (4000 mi).

Repair

• If the final evaluation shows more than 0.946 liter (1 qt) used in 3200 km (2000 mi), follow the published symptom diagnostics in the appropriate Service Manual.

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  8. If the final evaluation shows that the engine uses more than 0.946 liter (1 qt) in 3200 km (2000 mi), follow the published symptom diagnostics as described in the appropriate Service Manual.

Caution

• The accepted rate of oil consumption is 0.946 liter (1 qt) in 3200 km (2000 mi).

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  The accepted rate of oil consumption for engines used in the vehicles referenced is 0.946 liter (1 qt) in 3200 km (2000 mi).

• That rate does not apply to vehicles driven aggressively, at high RPM, at high speeds, or (for trucks) loaded; consumption under these conditions will be more.

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  Important: This rate does not apply to vehicles that are driven in an aggressive manner, at high RPM, high speeds, or in a loaded condition (for trucks). Oil consumption for vehicles driven under these conditions will be more.