If there is no signs of external leaks, then it is going through the engine. Has there been any repair history of oil usage concern with the dealer, while the vehicle was still under warranty? There is a bulletin that involves some checks, and states that if the oil consumption is determined excessive after a consumption test, replace the piston rings and valve stem seals. I will give you the bulletin for reference.
#PIP4439: HFV6 Oil Consumption - keywords 2.8 3.6 rings seal smoke valve - (Jul 23, 2008)
Subject: HFV6 Oil Consumption
Models: 2004-2007 Buick Rendezvous,
2005-2008 Buick Lacrosse, Allure
2008 Buick Enclave
2004-2008 Cadillac CTS, STS, SRX
2008 Chevrolet Malibu, Equinox
2008 GMC Acadia
2007-2008 Pontiac G6
2008 Pontiac G8, Torrent
2007-2008 Saturn Aura, Outlook
2008 Saturn Vue
with LP1 2.8L, LY7 3.6L, or LLT 3.6L V6 engine
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Some customers may comment of excess engine oil consumption.
Verify the oil consumption concern following bulletin 01-06-01-011D. In addition, check the engine air filter and replace the air filter element as necessary. Care must be taken to ensure that the air filter and air filter box are reassembled correctly so that the filter and air box seal and prevent foreign particles from bypassing the filter. Check for signs of foreign particles bypassing the filter and getting into the engine, such as dust or dirt in the air intake duct or on the throttle body. If dust or dirt is found, look for the source of the leak, such as incorrectly assembled air filter/air filter box, loose clamps or incorrectly assembled joints at the air duct, leaking sensor gaskets, damaged duct parts, etc. And correct as necessary.
If oil consumption is in excess of the guidelines in bulletin 01-06-01-011D, replace the piston rings and valve seals.
Thursday, April 15th, 2010 AT 11:59 PM