The oil stays clean in my 85' 300sd for about 2 weeks and then starts to darken never had it go black instantly. I change oil and filter every 3000 miles with Rotella 5w40.

Do you drain your oil cooler as well when you do an oil change? I don't and my oil is black in 30 seconds after a change. I change mine every 3-4k miles with 5w40 Rotella.

Nope cant say that i do that. When i first bought the car the oil got pretty black soon after a change but that went away after the 2nd or 3rd 3000 mile change with the rotella. But it was never instantly .... maybe a few hours of driving after. I am pretty picky about 3000 miles though it usually gets done around 2900 dunno if that has anything to do with it. I also run b100 in the summers and keep fresh fuel filters in it (every 3rd oil change, or when changing back to dino diesel in the winter).

this thread is funny