GM Service Manual Online
For 1990-2009 cars only

An engine that has excessive oil consumption uses 0.9 L (1 qt) of oil, or more, within 3 200 km (2,000 mi). The following list indicates the conditions and corrections of excessive oil consumption:

    â€¢ An improperly read oil level indicator dipstick
       - Inspect the oil level while the vehicle is parked on a level surface.
       - Allow adequate drain-down time.
    â€¢ Improper oil viscosity
        Use the recommended SAE viscosity for prevailing temperatures.
    â€¢ Continuous high-speed driving
    â€¢ Severe hauling, such as a trailer. This causes decreased oil mileage.
    â€¢ A malfunctioning crankcase ventilation system
    â€¢ External oil leaks
       - Tighten the bolts, as needed.
       - Replace the gaskets and seals, as needed.
    â€¢ Worn or omitted valve guides and/or valve stem seals
       - Ream the guides.
       - Install oversized service valves and/or new valve stem seals.
    â€¢ Broken or worn piston rings
    â€¢ Improperly installed or unseated piston rings
    â€¢ Improperly installed or improperly fitted piston
    â€¢ Plugged cylinder head gasket oil drain holes
    â€¢ Damaged intake gaskets