My owners manual calls for 3 3/4 quarts of oil with a filter change. but often when I go to change the oil only need 2 1/2 to 3 quarts before the dipstick is between the high in the low. Why does this happen?? I use mobil 1 advanced feel economy synthetic oil and an extended performance or filter. i've been changing my oil every 10,000 miles with filter change.