General Motors Vortec line of V-6 engines commonly suffer from problems with excessive oil consumption and engine knocking. Knocking problems are particularly prevalent in Vortec engines used in trucks and SUVs built during the late 1990s and early 2000s. Some Vortec V-6 engines also develop problems with their camshafts, though this seems to be more common among Vortec engines used in industrial applications rather than in passenger vehicles.
Severe knocking issues are most common to the L35 and LF6 Vortec V-6 engines built between 1996 and 2002, while oil consumption issues are more common in the LU3 engine built from 2004 to 2009. Owners of vehicles with Vortec engines affected by knocking issues report that the problem seems to occur after the engine has had some time to warm up or during acceleration. The cause of the knocking issue has not been definitively determined, but some owners report that replacing the pistons in the engine may address the issue. Owners with newer Vortec engines that consume excessive oil report that these engines may consume up to two quarts or more of oil between service intervals. The Active Fuel Management selective cylinder shutdown system is suspected to be one of the causes of this issue, and some owners have reported that disabling this feature can reduce oil consumption substantially.