mentioned by mc....
sometimes I'll check my oil and the level will be low,like maybe a quart and a half low, so I'll wait a day and the next time I check it it is right where it should be. I'm starting to get used to waiting a day or until after the next time I drive the car for a second reading,
After the motor's been running, it takes time for the oil to run back into the sump; that's probably why you're getting a "low" reading one day and a "fine" the next. Wait at least 15 minutes or so after you shut down to make sure you get an accurate reading. Too much oil can be as bad as too little.
On your original question, I don't use synthetic, but my 99 SVT does burn about 3/4 of a quart between changes. Has done this since new.
