Another Motor Oil Topic

I changed the oil in 3 of my diesel pickups over the past couple of weeks and it got me thinking about oils and how they work. Truck #1: 1982 GMC w/ 6.2L diesel
Truck #2 1994 Ford 7.3L Powerstroke
Truck #3 2001 Ford 7.3L Powerstroke
I use Rotella 15w-40 in all 3 trucks and use Purolator filters on all 3 as well. I change the oil at 5k mile intervals.

The thing that got me thinking was the condition of the oil at the end of the 5k mile period. I know diesel oil will get more black than gas engine oil. The oil in the old gmc will be as black as coal while the powerstoke engines oil will not be near as black. For that matter, I can check the oil in the gmc after only 50 miles and it is as black then as it will be after 5k miles. All the while, the powerstoke engines gradually darken. Most of the way through the 5k mile oil change, you can still see the markings on the dipstick through the oil, not the case with the gmc.
The gmc is on its second engine since I have owned it. This engine has only 43,xxx miles on it. The oil looked the same way with the old engine which was wore plum out when I got it. So I cant say the powerstroke,s are still good and tight and the 6.2 is wore out. I've never saw a diesel engine turn oil this black that fast. The oil is so black it will stain your hands. It washes off with alot of gojo but using a rag wont begin to remove it.

Another thought about oil, when I was in trade school one of the instructors had just bought a brand new (at the time) 1997 F-250 powerstroke. He and I got to talking about oil one day. He said he uses Texaco Ursa (sp?). I had never saw it on the store shelves anywhere and still haven't to this day. He said that the oil is just as clean after 5k miles in his engine as it was when he poured it in. Interesting. ...

So here are my questions
1. What would cause my 6.2 diesel oil to be so black so fast? Would it have to do with emissions back in that era, more soot? The EGR system?
2. If the Ursa oil stays clean, does that mean the detergents arent working properly?

on edit (not that this matters) all of these trucks might consume 1 qt. Of oil in the 5k mile period.

Edited by David G. - 22 Feb 2015 at 6:57pm

More blow by makes oil blacker.

You may want to pull a sample the next time you change oil (let a little warm oil drain out before catching the sample).

http://www.blackstone-labs.com/

The test kits are free.  A basic analysis is $25 plus another $10 for a TBN analysis (good idea to do).  The kits can be mailed back using the USPS. 

Ok. Thanks for the comments. I suspected that the older engine had a lot to do with it.

Now what about oil that stays clean after 5k in a diesel? Is the detergent working?

And in the case of my idi International made the ring design sorta wacky and they produce more blow by than others.