I've gone and tried synthetic on several of my engines in differant vehicles and haven't really been sold on it for the kind of driving and use that I do, but I do really like to use high quality oil. I tried out Chevron Delo 400 15W-40 in both my Stovebolt and my BMW. I've found that the valvetrain runs a lot quieter and it's cleaned out some of the sludge under the valve cover. It seems to have good consistant wear properties and isn't any more expensive than most name brand oils, and it doesn't leak out of iffy seals like synthetic does. It is rated for both gasoline and diesel engines. Shell Rotella is also a good oil, but I haven't found it to be as commonly available as Delo. I've been using it on 10,000 mile change intervals in my BMW for the last 80,000 miles (it has 175,000 miles on it) and it runs just great and passes emissions tests reliably. The BMW six has 7 main bearings and an oil cooler. I don't treat the BMW kindly either, I drive it daily in mixed traffic and rev it to high RPMs whenever I feel like it. When I ran Valvoline in it the oil was done (stinky and black) at 5k miles.
