They can nail you for WMO too unless you can prove the sulfur content is low enough.

 

If they do check you on WMO, act all surprised and concerned, as in "what is that awful black-looking stuff, how could that be getting in my fuel" and the dipper-man will get all mechanical and tell you that the diaphragm in your lift-pump is probably ruptured and sucking oil into your fuel, "better get that fixed".

 

I use additive for the lubricity. Run winter additive when I have to for temps. Used Lucas for 2 years less smoke. After extensive reading on the lubricity of bio-diesel decided to switch to Soy cooking oil for additive at same mixture ratio. Have now done that for 300k (walmart at $6/gal.) Just overhauled the injection pump due to external leak and noted that internal parts showed no sign of wear at all at 600k I beleive the ulsd caused the leak in my pump but am glad we went in since I had a broken spring from metal fatigue.

 

One thing I have found since running used motor oil in the tank, it always looks black. Can't hurt to give it a try. Even if it is the used oil out of your truck.

Just something to think about and give it a try.