black oil non egr isx500

[ktbtrucking]

hello all,

have a non egr isx500 with 1.2mil miles and made around 50kmiles on it so far
popped up a head cover and front cover at repair shop and I ve been told it looked really clean.

Problem is oil is black even when I change it. I assume that around one gallons is left during oil change. But after the oil change it is black. I have other trucks and I know what black means.

I did oil change twice by myself and twice and Speedco Gary,In asked for oil analysis,but their machine is mostly down.

Any thoughts?

I have two other isx with egr engine 1.1-1.2 mil and the oil there turns dark brown but never black.

I have time and would like to keep the engine running so please advice on some steps I can take and extend my knowledge on this.
Thank you.

Edit: I can change the oil twice the same time if it might help.Also dropped oil pan at last oil change there was nothing at the bottom of the pan too.It looked really clean.