so I bought a 2010 F-450 with 6.4 and 84k miles a few days ago. the oil was pitch black so I changed it along with all the fluids. drove the truck 2 hours and the oil is black again. is diesel engine oil black by nature or does this thing need a flush?

 

Won't stay honey colored like a gasser, no.

 

Don't worry about black-ness, it doesn't mean anything. The only way to know how your oil is doing is with an oil analysis.

As Ted mentioned, it turns black quickly in a diesel engine for some reason. We used to have 30,000 mile oil change intervals in the road tractors I used to drive. After a few thousand miles the oil was as black as the tires, and we put 25-35,000 miles on the oil after that point. Never had an engine problem, I turned my oldest truck in at 543,000 miles. Much heavier duty engine in a different application, but the point is the same. Don't worry about the color of your oil!

 

It turns black as coal right away, doesn't it? It all looks the same.

The Army had an oil analysis program when I was participating and a couple of the boys down at our motor pool (hot rodders, naturally) had gotten tired of pulling samples from all the trucks as it was kind of a PITA so, instead they just filled all the sample bottles for the entire motor pool (maybe 50 or so) out of one single truck. Oops!

Folks at the lab were Not Amused, and the young troopies got in big trouble for that, LOL

 

Turns black in all of the newer ones, even my 6.7 turns black almost right away.

 

It is the amount of blow-by that causes it, as I understand it. I'm new to diesels as well and was trying to research this topic. Because of the compression ratio in a diesel engine, a lot of pressure makes it past the piston rings.

"In the true diesel engine, only air is initially introduced into the combustion chamber. The air is then compressed with a compression ratio typically between 15:1 and 23:1 resulting in 40-bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.40 MPa; 120 to 200 psi) in the petrol engine."

https://en.wikipedia.org/wiki/Diesel_engine

 

the 6.4 has a compression ratio of 17.5:1 and my oil is charcoal color immideately upon 1st startup.......thinking it needed a flush....I did that and used new oil again and once again the oil was charcoal color upon 1st run.

I have a vmax motorcycle that has and 11.5:1 compression ration and the oil is tea color after 2500 miles.

 

6.4 also uses a keystone ring in the top of the piston. It is loose. Designed to create the seal when the motor is working hard.


So there will be more blow-by at idle then you would think.


Heavy boost motor, designed for a truck application.