For a truck like yours, it's already been proven that those IDIs will run crazy amounts of miles on regular oil. I don't see much reason to deviate. I've seen a 6.9 IDI at 751k miles and still getting along fine running conventional 15w40 Rotella and getting an oil change every 8k-10k miles (good amount of miles between, but the miles were also getting put on it pretty quickly). I wouldn't mess with what's been working, especially in a case like that.

 

One thing to remember is that diesel oil like shell rotella is a much more robust oil additive wise, than conventional dino oil. It HAS to be that robust to last in the hot sooty diesel conditions. Nothing wrong with using it in a gasser!

 

seems like one things been forgotten (forgive me if someone has said it), and its the fuel economy increase of synthetics. you can run conventional "cuz it does the job", which it does, a good conventional wont lead to rapid failure because of its usage, but it still isnt as good as synthetic in other realms.

yea, diesels like to run forever regardless of whats in there, but setting fuel econ aside i run synthetic for my turbo just as much as anything else.

 

I've only tried synthetic in one vehicle (Chevy 5.3), but I didn't see any MPG increase.

Have you experienced increased fuel economy?

 

did you run synthetic in everything?

i cant note synthetic changes one for another, because ive never tested each component of the drivetrain with one type of oil and then another.

i can say this, with stock injectors (and modifications directed toward mileage) in my dodge i always averaged 22-25 mpg with mixed driving. all synthetic in the drivetrain from front to back. that cannot be achieved with the truck stock. i cant attest to which component, run with synthetic, nets the best results but when you combine the gains from each component it becomes substantial overall.

i have, however, dyno'd cars withi conventional and then synthetc, and there is always a gain to be had by doing the conversion. more power, less friction, more mpg. drivetrain losses are also combated by the conversion as well, further solidifying the proof that synthetics net better fuel economy.

 

I'm sure I could do at least 5k between changes if I wanted. It doesn't get a whole lot of miles though, I've had it since February and I've only put about 2500 miles on it. I don't really like the idea of leaving oil in there for too long, especially with a lot of short drives.

Besides, like I said, I've never heard of an engine going bad because the oil was too clean. It's nearing up on 300k miles, so I'm willing to pay a bit extra to keep my engine out of the graveyard. Oil is a LOT cheaper than a rebuild!