Grand Prix 3.2lV6

• Automatic transmission
• 35,000 miles

I purchased the vehicle with 28,000 miles on in June of 2010--but I've noticed that at every 3000 mile oil change there is less and less oil in the vehicle--I typically want go over 3000 miles prior to getting a oil change--I had the oil changed on yesterday even though i was only at 2700 miles--but I checked the oil earlier in the day and noticed that it was more than a quart low and very dark in color--there are no signs of leakage and the vehicle doesn't smoke--but I know that when my warranty runs out I will be stuck with this huge bill---I spoke to a fellow grand prix owner and he stated that his vehicle is also a oil burner and he has gone to changing it every 2200 miles and that he has to use dura blend oils only---what is the deal? Am I about to lose an engine?