By black diesel, I assume you mean WMO.

Once upon a time, I read a cummins service bulletin that said WMO up to 10% was ok. Full tank of fuel and the WMO from an oil change.

 

You are filtering it first right?
Even my first gen didn't like WMO straight from the drain pan.. too much sediment and particulate matter..

 

WMO was probably OK for the earlier diesels but I would never put it in a common rail.

 

At one point, I had a cummins service bulletin that said it was GTG on my (03-06 at the time) truck... I'll have to find it.

To each their own... I've seen guys pour all kinds of crap in their tank and never have a problem, and guys that buy fuel only at truck stops and not put anything else in have all kinds of problems... it's a roll of the dice sometimes.