I unscrewed the oil fill neck from the valve cover on our 1998 f-150 company truck and was surprised to find the area very free of varnish or sludge. It was so clean that even after runing my finger in it came out very clean- with only the oil and no deposits. Insteresting that the only oil ever run has been Motorcraft conventional oil, 10-30 or 5-30. Motor is now over 140,000 miles. Seems to me with proper drain intervals a good conventional oil does well. The motor runs like new. This gives us dino fans more hope than ever.