hello,

My girlfriend has a 2007 Mazda 6 with the 6 cyl engine. When i picked her up, i also picked up the responsibility of changing her oil. Since i started, i noticed that it is consuming 3-4 additional qts of oil every 5000 miles. It has 85k miles, and this just doesn't seem right. I use full synthetic oil, no white smoke, no smell of burning oil, no puddles of oil.

On another note, one of the O2 sensors is in fault (may or may not be related to the oil possibly burning).

Any ideas why this is happening? Should she dump this thing now? Thanks alot!

 

First thing I would do is change the PCV valves. Mazda never changes them. This is the situation where you change it. Monitor it after that. If it improves, use a little thicker oil. You are due to change spark plugs as well. When you change spark plugs, do a compression test. This will let you know if dumping the car is required.
If you change O2 sensors, get a backpressure test done on your exhaust: this will tell you if your pre-cats are fubarred. How to check your vehicle's catalytic converter. - YouTube Video, go about 30 secs in video.
Reasons For A Converter Failure

This is exactly the reasons why the PCV valve and the spark plugs should be changed @ 60,000 - 70,000 miles. Personally @ this mileage this would be my 2nd PCV valve change.

 

galligator: What's the code you are getting?

As Noggin suggested, the oil may be blown out through the PCV system. Easy check: Is the PCV hose oily inside?

If the piston rings are a bit sticky they could allow blow by and that would increase the flow through the PCV. A "seafoam" treatment or "Lucas Oil Fuel treatment" could help a bit in that situation.

A quart per 1000 miles is a bit much but it is not a death knell either. After all it runs.