Bought this car in Sept. 2007 from a Dealership after they did an oil change, new brakes and tires. After putting around 1500 miles on the car the engine started pinging. Checked the oil and low and behold it was almost 4 quarts low!!!!! My first gut reaction was that the dealership did not put in the proper amount of oil during the change. I gripped about their inefficiency but they denied doing such a thing.

After topping off the oil I started checking the level about every 500 miles and noted that it was using more than a quart driving in the city. On interstate trips of around 500 miles it uses around 2 quarts. This has been going on since the day I purchased it and GM will not do anything about it. I've taken it back on many occasions to the dealership and have had discussions with GM to no avail.

I have researched this problem with the 3.6 engine and have found that many many people have had similar problems. Some have even locked their engines up not knowing they were out or almost out of oil. Of course there is no low oil warning light either. The most likely culprit are the rings that were pitifully engineered in that engine. CTS 3.6 owners from 2003-2007 should ban together and bring legal action against GM for this very serious problem that could cause a fatal accident if not already.

Update from Jul 30, 2014: Each time I drive my 2005 Cadillac CTS to visit my grandkids ( 300 miles one way of interstate highways) I have to add at least 1 1/2 quarts of oil after arriving and after coming home. This has been occuring since I purchased the car in 2007 with around 30000 miles on the odometer. The car does not smoke and it has never leaked oil. GM has not taken any responsibility for this condition. There are so many complaints online of this happening to others with this 3.6 L engine that something should be done about it. Engines are going dry of oil while on interstates and locking up and GM is blaming the owners for not checking their oil. A new purchaser of one of these cars would not know to check after less than 1000 miles of driving to see if there was any oil left in the crankcase!!!!! GM, DO A RECALL ON THIS SERIOUS PROBLEM!!!!!