Had an 03 5.9 in the shop yesterday with about 85K on it. One of the checks I do is to check the oil. It looked like it just came out of the bottle. No black soot. When I change my oil every 5K its pretty much black after I run it and double check the level. I looked for a bypass filter and saw none, and I think the oil filter was a Fram. When the owner got there, my boss asked what was up (he's got a 5.9 also) and all he said was that he runs 15w-40 Synthetic Rotella. He also said its been in ther for about 2 weeks (plenty of time to turn black if it was going to), and he changes it every 7500 miles.
So does the synthetic run cleaner or ???????

 

Difference between the 03's and and the 04.5's and up. Do a search. Lots of good info on why your oil gets dirty so fast. And it had nothing to do with synthetic either.

 

It has something to do with the 3rd injection events on the 04.5 on up trucks. 03 and early 04 trucks don't turn the oil black immediately.

I've run regular and synthetic oil and they both turn black immediately upon crank up.

..

 

I believe the 3rd injection event creates much finer soot particles that slip past the rings easier, or something along those lines.

 

92 1st Gen is correct. There was a third injection event on the newer 3rd gens added to that higher rail pressure which assists in getting better mileage, but leaves very small soot particles that make your oil black. I have a FS2500 bypass filter, and in a long conversation with Randy at Filtration Solutions, he said that he had gone down to less than one micron filter element as a test and the soot was still there, which is the cause of the black oil.