Oil sample not looking good.

[JimT]

Wow, 36,000+ miles between changes!

I've been getting averages between 7.8-8.0 mpg for the past year and I still get nervous when I push my oil change from my usual 15,000 miles up to 16,000 miles because I'm still on the road (I do my own changes at home). If your down in the 6's then you should be looking at 7,000-10,000 mile intervals. Start lower just because the truck is new to you and could use the help flushing the neglect of is past life. 10,000 mile intervals would be more normal for mid 6's to low 7.

Oil samples are good, but they are really only a good tool for detecting changes over time. You can't usually look at a single sample in isolation and expect to devine what's going on. My opinion, best to sample at every oil change and watch the trends. Make notes about anything that could have had a significant impact on that oil and factor it in to your own analysis. That being said, don't ignore the other advise from here in regards to the samples posted.

When you settle on your preferred oil, be it Rotella (the most popular on this site) or Delo (my personal preference for my engine) also consider availability. Pick one and stick with it knowing that either you or your preferred shop will always have and use the same oil every time.

You might think a big fleet maintained vehicle would have a good solid service history (that was my naive thought once) but that is far from reality. Nearly all big fleets (including places like Ryder and Penske) adopt maintenance schedules that meet the bare minimum to keep the average truck running through their planned ownership period. So, if they plan to sell it at 500,000 miles then they will only do as much as needed to ensure it's useful life makes it to that point, and not a dime more. This is why we see ridiculous oil change (and grease too) intervals of 30,000+ miles and fleets using 10w30 instead of 10w40 (because it slightly increases fuel mileage at the expense of engine life expectancy - which is not their problem after they sell it). They buy trucks new at quantity discounts, milk them for every penny while equipping them with careless company drivers that have no stake in the equipment. Then turn around and sell them when they hit the predetermined end of life or when they show the first signs of an impending major repair. (The worst are the companies that thrive on offering these trucks as lease purchases, knowing full well that the financial burden will likely prevent the purchaser from completing the lease term.) Anyway, getting a little of topic here, sorry.