Just a comment because I am no expert on oils by any stretch. Please comment George.... When I change my engine oil (2,500 miles) it is ALWAYS very dark due to contamination from combustibles, water, and dirt (over time). I have used Mobil 1 and Syn 3 as far as synthetics go and it's always "dirty". However, if you look at a smaller sample of the oil it's not as "dark" as it looks while coming out of the drain hole. I fully understand how the synthetics can go for many more miles and not break down but no matter what oil you use, it's going to get contaminated in an "unsealed" motor. The primary and tranny oil always comes out looking like it just came out of the bottle...almost. Just me but I will continue to change engine oil at 2,500 - 3,000 regardless of what I use....because I know for sure that it is always being contaminated.
Semper Fi,
Steve...Pensacola
USMC 1972 - 2003