First I'll answer the question, then I'll ramble:
I went 12655 on my Delvac 1, with one filter change at 5721 miles. I'm planning on similar intervals with Amsoil HDD 5W-30, but only if Silicon stays reasonable after I start driving dirt roads again in the Spring.
Oil Analysis results on the Delvac 1:
Truck miles / Oil Miles / Si / Fe
16845 / 5721 / 10 / 34
23779 / 12655 / 15 / 71
I changed filter, added 1. 5 qts, removed
Psychotty and added foam pre-cleaner at about the time of that first sample. I do not have a bypass system, and as you can see both Si and Fe continued to increase but at a lower rate.
My first reactions to these sample results was considerable concern. Too much Si, way too much Fe. But all my other wear metals were low, so ??? The good news was that it looked like the foam pre-cleaner had reduced my Si intake and Fe wear rates, so maybe my "problem" was under control. Then I went back and searched for all past posts with actual oil sample results, and calculated for each one how much Si and how much Fe per 5000 miles. After making that adjustment, guess what? Newer trucks always have higher Si and Fe, older trucks have less.
All this confirms what others on this board have said: These trucks take a LONG time to break in. My rate of Si and Fe weren't going down because my Delvac was getting better as I put more miles on the oil or because of the foam pre-cleaner; they were going down because my truck was still wearing in at ~20,000 miles.
I changed to Amsoil, and I'll bet $100 my next analysis will show reduced Fe wear. Now, here's where it gets tricky. I'll also bet $100 that I could have stayed with Delvac, and my next analysis would still have showed lower Fe, because my truck is still breaking in! (I changed to synthetic at 11124, if anyone was wondering. )
All you folks who believe your wear went down when you changed from Brand X to Brand Y, or from 15W40 to 5W30 even within the same brand, please do an experiment for us: Change back to the previous oil for just 5000 miles, and tell us if your wear goes back up, or does it continue to go down because even at 60,000 or more your truck is still getting better with age?
I'm going to continue to do oil analysis for benefits like knowing if my air system develops a leak, but I think I will have to take the results with a grain of salt and not read too much into them. Heck, maybe I'll even take my own bet and switch back to Delvac at the next change just to see what happens. Your results may vary, this is JMO.
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2001 ETH, QC, LWB, 4WD, 3. 54, SPA Pyro & Boost, K&N RE-880 w/foam pre-cleaner, ARE Z-series Cab-high shell, Rear ARB locker, and all kinds of synthetic fluids...
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