I recently changed oil and filter on my daughters riding mower. The owners manual states oil capacity w/filter 56oz and without filter 48oz. Since I changed oil filter I thought it would take 56oz so I put in 1 full quart 32oz and decided to check dipstick and it's showing the oil to be about and inch over the full mark. I then decided to measure the oil that drained out and it was about 18oz. Any thoughts as to what's going on ?