2007 Using Oil

You only checked the oil one time after you did an oi change. That's really not enough times to indicate a trend. Several things could have caused you to read slightly lower after you drove the car for a while just after you did an an oil change.

Check the level weekly. Is it continuing to drop or maintaining at the level you first checked it at after the change (your "600 mile" point). Check the level a couple more times in a couple more weeks. See if there is a trend before worrying about it.

 

Use the dipstick to judge the oil used, it's much more accurate than trying to judge how much oil was drained. Checking the dipstick just before each oil change is an important way to track oil consumption.

Could be worthwhile getting the PCV valve tested/changed if it hasn't already been done.

There are a number of reasons why oil consumption may appear to be greater than it really is. One is when you don't re-check the oil level after running the engine for a short while after an oil change. You may have very carefully re-filled to the upper mark at the oil change, but unless you also checked again after the engine was run for a few minutes then that could have dropped to 3/4 or less. The reason is that after an oil filter change there are usually "dead spaces" in the filter and oil galleries that don't get properly refilled until the engine is next started.

Another possible reason is not waiting long enough for the oil to drain back before testing, giving an artificially low reading. In any case a little bit of oil consumption when you're over 100,000 miles is not too uncommon and usually very manageable. Don't hesitate to check regularly and do mid interval top ups.

 

Uart I agree and engine wise the PCV valve would be my first port of call.