DD15 oil change?

I believe the OEM recommended oil change interval is 50k. So you would be safe with 35k.
I'd run mineral oil and monitor your oil consumption. Then switch to synthetic and see if it goes up.

 

Yes, 50k is OEM interval. You should do an oil sample analysis and see where your at as far as wear metals, etc.
I use Polaris Labs.

 

Don't use Speedo for oil analysis, it's worthless.

 

Don't use Speedco for anything, IMHO. Not that Petro/TA, or the other truckstop shops are any better. A good shop is hard to find. Even see that list that a thorough PM is supposed to cover? Find a shop that actually does that. I use Mobil Delvac straight oil, Detroit fuel and oil filters in my 60 Series 14L. 1,100,000 so far, clean oil analysis.

I tried that synthetic oil for a go-round. The only thing I noticed was how expensive that stuff is. My truck didn't show any difference. I do PM's around 20K, more or less. I don't care who says what, more than that just doesn't make sense. I guess all that fried black parafin in the oil is a lubricant? I don't think so. Then there are the combustion by-products, including acids that etch metals and other parts. 50K? Not for me. Best

 

I agree with your entire post. I have never realized a fuel mileage difference or engine life variance by using synthetic oil.
If you don't mind my asking, have you had to replace many EGR valves or coolers on that 14 L ?

 

Not the EGR, but the cooler went south around 900,000. Geez, can't get good components any more.

I had to have a new DPF filter and accessories, around $5K, but smooth sailing in the year since. I have replaced a lot of the peripheral components, last year was expensive, but the truck earned more than it cost. We've read a lot of horror stories about DPF, EGR and I'm sure many of the problems are unavoidable due to design or quality. But since I started taking my truck with that 60 Series to a Stewart & Stevenson shop here in Albuquerque (Detroit specialists) I've had good service, no issues with the things they've done, and they actually inspect my truck for upcoming issues and discuss them with me. So I think a good shop is a really important piece of the puzzle.

 

The conventional oils are fine for OEM recommended intervals. That being said, I have gotten fond of synthetic blends. Hardly much more than conventional pricing and a little bit of an edge in protection. My Detroit 12.7 has been on a 10w30 syn blend for a while. As good or better oil samples compared to the 15w40 it got before. And it has 528,000 now on the factory reman. See for yourself. Top two samples using 10w30, the bottom two using 15w40. All of the new OEM engines are being factory filled with 10w30 now.