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In my 6.0 4x X. Mileage was 4,750. Was gonna wait 'til at least 5k but had the time today.
The engine didn't burn a drop of oil as far as I could see. The stuff was still sorta clean.
About 1500 miles of this was towing a light (5500 lb) travel trailer.
Reason for this post is to say that I'm not going to change the oil any more often than 5k if I've been towing. If there's a dry spell (no towing), I intend to let changes go 'til 7k miles. At the next change I will send an oil sample to the Blackstone Labs, and see what shows up.
I do think most of us are a bit too conservative re oil changes. Kinda like throwing your bucks away.
My two cents on this subject. (certainly not worth any more than that)
The 6.0L motor shears down the motor oil (reg & synth). I would change at 5,000 miles on a regualr basis no matter what.
I changed out the first 2 oil changes at 3,000 and 6,000 (3,000 intervals) to get out all assembly dirt from when the motor was casted and break-in particals.
All Blackstone oil reports for all have shown the shearing down of the 15W-40 oil to that of a 30 weight... 7,000 miles is to long of an interval.
The spec on the 6.0 for normal duty is 7500 miles (up from 5000 miles on the 7.3s). I've run a *lot* of oil through our '97 F250HD, and the 2000 X before we traded it, all at 5000 mile intervals, so I'm pretty familiar with what the oil looks like at that point and how the engine behaves as the oil gets old, etc. So after the first few short oil changes on the '03 during break-in I let it go 7500 miles to the next change. Yikes, that stuff was like water coming out of there. Very scary. I went back to 5000 mile changes on it ever since, and I'm much happier with the look of the used oil coming out now - it still looks like it could be lubricating and protecting my engine.
In the beginning, I changed my oil every 3K miles (first 9K), then extended it to 5K this last change. Sent first sample to blackstone at 12K. Everything came back great with very little fuel, shearing, and good filtration. They said I had plenty of life left in oil. Switched to Mobil 1 Synthetic and sent sample up with 4600K on oil. Said they were happy to know I have not changed oil and to leave it in another 3K, send up sample, and they will let me know how it's doing at that time. Also said engine is breaking in better than average. The only thing I do regularly now is change the filter.