I have a friend who purchased an abused honda accord 4cyl (@ 60K and now has 118K) and the valvetrain (what I can see through the oil fill hole) is rather badly varnished. Aparrently the previous owner was REALLY slack on oil changes and other maint as the dipstick is coated in varnish up to the top of the handle. They cannot afford the 2 $25 auto-rx treatments, but do change the oil with 10w30 at 3-4k with either supertech syn blend or syn and a supertech filter. What should oil they run in order to clean out some of the crud? I've heard rotella and mobil/delvac 5w40 have better detergency than regular oil. Any opinions? Is it safe to run a 5w40 oil in a 4cyl that uses 10w30? Will it affect gas mileage a lot? Thanks for the advice.