The reason Mobil 1 is black when it comes out of your engine is that is has been cleaning carbon and blow-by buildup, like it is supposed to. I work for Mercedes Benz, who use mobil one in all their engines (including the 370kw twin turbo V12) and they never have a problem with their engines at all.
On the same note, if you have an older engine which has been running for 150,000 kms or more, and is used to running with the carbon buildup, do NOT run mobil one. It will clean the engine down, like it is supposed to, but then the motor will blow smoke and use oil because the clearances are too large in the engine now, courtesy of the carbon being cleaned away.
I have seen engines requiring rebuilds because of this (hyundai excel, and toyota corolla).
Mobil one is a good oil, but it needs to be used for the lifetime of the engine for it to work properly.
I will not be running it in my GTR when it lands for these reasons, but if i rebuild the engine, then i will run mobil 1 after the running in period.
Just my 2 cents
