We just recently took a 2500 mile trip in my 2011 S80. When we got back, we were a little less than 2 quarts low on oil. Is that normal to burn that much oil? Granted, it was 2500 miles in a week.....I know when I did my oil change, it was about a quart low...and that was at about 3500 miles of 120 mile a week travels. Thoughts?