I bought my car in March of last year with 103,000 miles on it. It would take 1 quart of oil (Castrol GTX 5w-30) between oil changes. Now it has 123,000 miles on it and a mild turbo setup, and oil consumption rose to 2 or more quarts between oil changes. My car doesn't leak, or smoke that I can see. Where is the oil going? Is it being burnt up due to bad rings? Or could this be a problem with the head? How do I determine the cause?

 

Based on the character of your observation, I presume that the oil is not leaking out from the engine externally.

The most common causes of internal oil consumption would be, in no particular order:

1- Worn rings
2- Faulty valve seals
3- Faulty PCV system

Rings can be diagnosed to some degree of accuracy by performing a compression test. If compression is initially low but increases significantly after introducing a small amount of oil through the plug hole, then rings are suspect.

There's no test that I'm aware of for valve seals, but a defect in this area will usually be accompanied by the production of bluish smoke just after the engine has been started after resting for a period of time.

It is possible that a fault in the crankcase ventilation system can lead to increased oil consumption, either directly through the intake, or indirectly by permitting crankcase pressure to decrease the sealing efficiency of the rings.

I would start with a compression test. It's quick, easy, and informative.

 

As always, joe pretty much sums it up. fwiw, +1

 

you can also still be loosing oil and not see it because it gets burned up in the cat.

 

how is your pcv/crankcase vent system routed, and what PCV valve are you using (and how old is it)? i had a lot of oil burning problems related to my catch can/pcv setup.

 

You can pretty much ppin point where the oil is escaping, if it's escaping, by perfoming a leak down test. If you don't know what you're doing have an experienced mechanic do one for you and pay him on the side to save some money. That should tell you.