Your diesel turns black because of a chemical reaction leaving the diesel with a black pigmentation.
Why Would Oil Be Mixing With Fuel In A Isx Cummins Engine And The Truck Keeps Shutting Down While Driving?
This is how works isx cummins ,it replace used oil engine with new oil from in side the engine -is like a tank-mixing used oil with fuel
Some of them automatically dump a quart of oil through the engine dude. Check your owners manual man. Its done on a timed system or something like that